Bosch 24I RSF User Manual

Bosch Group

24i RSF

WALL MOUNTED COMBINATION BOILER FOR CENTRAL HEATING

AND MAINS FED DOMESTIC HOT WATER

INSTALLATION AND

SERVICING INSTRUCTIONS

GC NUMBERS

N.G. 47 311 37 L.P.G. 47 311 38

BOILER OUTPUT

To Domestic Hot Water – Modulated Control

Minimum 7.5 kW (25,600 Btu/h)

Maximum 23.4 kW (80,000 Btu/h)

To Central Heating – Modulated Control\

Auto Range Rated

Minimum 7.5 kW (25,600 Btu/h)

Maximum 23.4 kW (80,000 Btu/h)

THESE INSTRUCTIONS APPLY IN THE UK ONLY

THESE INSTRUCTIONS ARE TO BE LEFT WITH THE USER OR AT THE GAS METER

This appliance must be installed by a competent person in accordance

with the Gas Safety (Installation and Use) Regulations 1994

1.1 Gas Safety (Installation and Use) Regulations, October 1994

all gas appliances must be installed by a competent person in
accordance with the above regulations. Failure to install
appliances correctly could lead to prosecution.

1.2 The manufacturers notes must not be taken, in any way, as
overriding statutory obligations.

1.3 The compliance with a British Standard does not, of itself,
confer immunity from legal obligations. In particular the
installation of this appliance must be in accordance with the
relevant requirements of the following;
Gas Safety (Installation and Use) Regulations 1994 as amended.
Current IEE Wiring Regulations BS 7671.
Local Building Regulations.
Building Standards (Scotland)(Consolidation).
Bylaws of the local Water Company.
Health and Safety Document No. 635 (Electricity at Work
Regulations).
The British Gas Material and Installation Specification for central
heating and hot water
It should be in accordance with the relevant recommendations of
the following British Standards.
BS6798:1987 Specification for installation of gas fired hot water
boilers of rated input not exceeding 60 kW.
BS5449:1990 Central Heating for Domestic Premises.
BS5546:1990 Installation of gas hot water supplies for domestic
purposes.
BS5440:1:1990 Flues and Ventilation for gas appliances of rated
input not exceeding 60 kW: Flues.
BS5440:2:1989 Flues and Ventilation for gas appliances of rated
input not exceeding 60kW: Air Supply.
BS6891:1988 Installation of low pressure gas pipework
installations up to 28mm (R1).
BS7593:1993 Central Heating system cleansing and flushing.
BS5482:PART 1 Domestic Butane and Propane gas burning
installations in permanent dwellings.

1.4 To ensure that the installation will perform to the highest
standards, the system and components should conform to any
other relevant British Standards in addition to those mentioned
in the instructions.

1.5 The appliance complies with the Essential Requirements of
the Gas Appliance Directive and other Directives currently
applicable.

1.6 This appliance contains no asbestos products.
There is no potential hazard due to the appliance being
electrically unsafe.
There are no substances used that are a potential hazard in
relation to the COSHH Regulations 1988.

1.7 The advice and instructions given in this document covers, as
far as possible, the foreseeable situations which may arise. Contact
Worcester Heat Systems Technical Helpline for advice on specific
installations.

2.1 This appliance is not suitable for external installation.

2.2 The appliance controls are set to provide a maximum output

of 23.4 kW for the domestic hot water and central heating load.

2.3 The control circuit provides direct burner ignition. A pilot is
not used.

2.4 PRINCIPAL APPLIANCE COMPONENTS.

See Fig. 1.
A low thermal capacity Gas to Water heat exchanger
incorporating an integral Hot Water heat exchanger to provide
domestic hot water.
Fully modulating controls in the central heating and domestic
hot water modes of operation.
An expansion vessel, pressure gauge and pressure relief valve.
A fixed by-pass for the central heating system.
A Temperature safety cut-out control.
A water flow regulator.
A standard telescopic horizontal flue assembly giving flue
lengths from 127mm to 350mm.
Optional extra extension flue kits to provide for flue lengths up to
2500mm.
An optional vertical flue kit to provide for flue lengths up to
3000mm including vertical flue terminal.
Optional facia mounted mechanical programmer.

2. General Information1. Installation Regulations

2

1. Installation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . Page 2 10. Electrical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 9

2. General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2 11. Installing the Appliance . . . . . . . . . . . . . . . . . . . . . . . . . . Page 11

3. Data Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 4 12. Commissioning the Appliance . . . . . . . . . . . . . . . . . . . . Page 16

4. Siting the Appliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 5 13. Instructions to the User . . . . . . . . . . . . . . . . . . . . . . . . . . Page 18

5. Siting the Flue. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 6 14. Inspection and Service. . . . . . . . . . . . . . . . . . . . . . . . . . . Page 18

6. Air Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 6 15. Replacement of Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 20

7. Sealed System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 7 16. Conversion Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . Page 23

8. Open Vent System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 7 17. Operational Flow Diagrams. . . . . . . . . . . . . . . . . . . . . . . Page 24

9. Hot Water Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 8 18. Fault Finding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 26

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19. Component Parts List. . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 34

Contents

Fig. 1. Water flow diagram.

Bi-thermal
gas to water
heat
exchanger

Automatic
air vent

Domestic
water flow
switch

Pressure
relief valve

Safety

discharge

Domestic
hot water

out

Domestic

cold

supply

C.H.

return

Sealed
system
expansion
vessel

Circulating
pump

Fixed
by-pass

C.H.

flow

2.5 ELECTRICAL SUPPLY

Mains supply: 230V ~, 50 Hz, 180 watts.
External fuse: 3A., Internal fuses: 2AT HRC(F1), and 1 AF (F2).

2.6 GAS SUPPLY

The boiler requires 2.76 m3/h (97.5 ft3/hr) of natural gas with a
calorific value of 37.78 MJ/m

3

(1014 Btu/ft3) or 1.07 m3/h (37.8

ft

3

/hr) of propane with a calorific value of 95.65 MJ/m3(2568

Btu/ft

3

). The meter governor should deliver a dynamic pressure
of 20 mbar (8in w.g.) at the appliance, equivalent to a pressure of
about 19-19.5 mbar at the gas valve on natural gas or 37.0 mbar
(14.8in w.g.) at the appliance for propane.
The gas meter and supply pipes must be capable of supplying
this quantity of gas in addition to the demand from any other
appliances being served. The table below gives an indication of
limiting gas pipe lengths and the allowance to be made for
fittings. Refer to BS6891 for further information.
The complete installation, including the gas meter, must be
tested for soundness and purged. Refer to BS 6891.

Note: Each fitting used in the gas line from the meter is
equivalent to a length of straight pipe which must be added to
the straight pipe length to give the total length.
i.e.: Bend = 0.5 metres, Tee = 0.5 metres, 90° Bend = 0.3
metres.

2.7 PACKING

The appliance and flue components are packaged separately.

2.8 GENERAL INSTALLATION

The appliance is for connection to a sealed system only.
The specified ventilation openings made into a wall or
compartment door must not be obstructed.
If the appliance is to be fitted into a compartment then the
compartment must conform to the requirements of BS 6798:
1987: Section 7.
Do not place anything on top of the appliance.
The clearances specified for servicing must be maintained.

2.9 FLUE

The appliance has a multi-directional fanned flue system.
The standard telescopic flue assembly length is from 127mm to
350mm.
Extension flue lengths available are from 350mm to 2500mm.
An optional vertical flue kit to provide for flue lengths up to
3000mm including vertical flue terminal.
A terminal guard, Type K2, GC 393 553, is available from Tower
Flue Components, Vale Rise, Tonbridge, TN9 1TB.
Do not allow the flue terminal fitted to the outside wall to
become obstructed or damaged.
A kit for internal fixing of the flue is available separately.

2.10 CONTROLS

The electronic control system and gas valve modulate the heat
input in response to the domestic hot water temperature and
central heating setting between minimum and maximum.
The Central Heating Temperature control knob provides for the
selection of domestic hot water only (Turned fully anti-clockwise)
or central heating and domestic hot water (Turned clockwise).
A facia mounted programmer is available as an optional extra. A
remote mounted programmer may be connected to the
appliance.
There is provision for the connection of a mains voltage room
thermostat and/or a frost thermostat.
The electronic controls prevent rapid cycling of the appliance in
the central heating mode.

2.11 SYSTEM NOTES
IMPORTANT

Check that no dirt is left in either the gas or water pipework as
this could cause damage to the appliance. The heating system
should be flushed and treated in accordance with the
recommendations of BS 7593:1992. Thoroughly flush cold water
mains supply and purge the gas supply before finally connecting
the appliance.
The water pipe connections throughout a sealed system must be
capable of sustaining a pressure of up to 3 bar.
Radiator valves must conform to the requirements of BS
2767:1991.
The relief valve discharge must be directed away from any
electrical components or where it would cause a hazard to the
user.
A drain cock to BS 2879 must be fitted to the lowest point of the
system.
For circuit design purposes it is important that due note is taken
of the information given in Table 3, section 3 relating to the
available pump head.

2.12 SHOWERS, BIDETS, TAPS AND MIXING VALVES

Hot and cold taps and mixing valves used in the system must be
suitable for operating at mains pressure.
Thermostatically controlled shower valves will guard against the
flow of water at too high a temperature.
Hot and cold mains fed water can be supplied direct to an over­rim flushing bidet subject to local Water Company requirements.
With all mains fed systems the flow of water from the individual
taps will vary with the number of outlets operated
simultaneously and the cold water mains supply pressure to the
property. Flow balancing using “Ball-o-Fix” type valves is
recommended to avoid an excessive reduction in flow to
individual outlets.

2.13 SAFETY CONSIDERATIONS

The appliance must not be operated in a waterless condition.
The appliance must not be operated with the boiler inner casing
cover removed.
Work must not be carried out on the appliance without the gas
and electricity supplies being switched off.
Checks must be made to ensure that the ventilation openings
made into walls and partitions are unobstructed and the correct
size.

2.14 OPERATION
Domestic Hot Water:

With a demand for hot water the burner
will light at its maximum setting and then automatically adjust
its output to maintain the temperature of the delivered water.
When hot water is no longer required, the burner will extinguish.
The fan and pump may continue to run for a short period to
dissipate the residual heat from the appliance.
Central Heating: With a demand for heating the burner will light
at its minimum setting and gradually increase to give a
controlled temperature rise. When the required heating
temperature is achieved the output of the appliance is then
automatically adjusted to maintain the temperature of the
system. The output can reduce down to a minimum of 7.5 kW. If
the system no longer requires even the minimum output to
maintain the desired room temperature the burner will
extinguish. The fan and pump may continue to run to dissipate
the residual heat from the appliance. The appliance will remain
off for a fixed period before re-lighting to automatically meet the
system requirements.
Domestic Hot Water and Central Heating: The appliance will
supply heat to the central heating system as required. A demand
for domestic hot water at a tap or shower will override the
central heating requirement for the period of the domestic hot
water demand. When hot water is no longer required the
appliance will return to the central heating state and its normal
mode of operation. The fan may continue to run to dissipate the
residual heat from the appliance as necessary.

2.15 DOMESTIC SUPPLY

Devices capable of preventing the flow of expansion water must
not be fitted unless separate arrangements have been made.

3

Total length of gas supply pipe Pipe size

(metres) (Ømm)

36912

Propane

Gas Discharge

1.5 – – – 15

Rate

8.0 5.2 4.2 3.6 22

(m

3

/hr)

15.9 8.8 8.5 7.2 28

Natural Gas

8.7 5.8 4.6 – 22

18.0 12.0 9.4 – 28

Gas

Discharge

Rate

(m3/hr)

The data plate is fixed to the inner casing cover.

3. Data Tables

4

NOMINAL BOILER RATINGS

OUTPUT INPUT (Net).

BURNER SETTING

GAS RATE

PRESSURE

kW Btu/h kW Btu/h m bar. in. wg. m

3

/h ft3/h

NATURAL GAS

7.5 (25,600) 9.60 (32,750) 1.0 0.4 1.01 35.7

23.4 (80,000) 26.05 (88,890) 13.6 5.4 2.76 97.5

PROPANE

7.5 (25,600) 9.60 (32,750) 3.5 1.4 0.39 13.9

23.4 (80,000) 26.05 (88,890) 35.0 14.0 1.07 37.8

Table 1

AVAILABLE PUMP HEAD

BOILER OUTPUT HEAD MIN. FLOW RATE

TEMPERATURE RISE

ACROSS HEATING

kW Btu/h Metres Feet L/min. Gal/Min. FLOW AND RETURN

7.5 (25,600) 6.0 19.7 9.8 2.2
11°C (20°F)

23.4 (80,000) 2.6 8.5 30.5 6.7

Table 3

SPECIFICATIONS

CENTRAL HEATING FLOW FITTING 22mm Compression
CENTRAL HEATING RETURN FITTING 22mm Compression
COLD WATER MAINS INLET FITTING 15mm Compression
DOMESTIC HOT WATER OUTLET FITTING 15mm Compression
GAS INLET FITTING Rc

1

⁄2inch
PRESSURE RELIEF VALVE DISCHARGE FITTING 15 mm Copper Tube
OVERALL HEIGHT (including flue turret) 960mm (37.8 inches)
CASING HEIGHT 800mm (31.5 inches)
CASING WIDTH 450mm (17.7 inches)
CASING DEPTH 360mm (14.2 inches)
WEIGHT(including water) 44 kg
INSTALLATION WEIGHT 39 kg
PACKAGED WEIGHT 44 kg
PRIMARY WATER CAPACITY 3.0 litres
MAXIMUM COLD SUPPLY PRESSURE 10 Bar (150 psi)
MINIMUM COLD SUPPLY PRESSURE (working) for max. hot water flow 0.9 bar
MINIMUM COLD SUPPLY PRESSURE (working) to operate appliance 0.1 bar
MAXIMUM CENTRAL HEATING FLOW TEMPERATURE Nominally 82°C (180°F)
OUTPUT TO DOMESTIC HOT WATER Modulating 7.5 to 23.4 kW
OUTPUT TO CENTRAL HEATING Modulating 7.5 to 23.4 kW
MAXIMUM DOMESTIC HOT WATER FLOW RATE (from the appliance) Nominally 8.0 ± 15% litres/min
EQUIVALENT DOMESTIC HOT WATER FLOW RATE TO GIVE A TEMP RISE Nominally 11.2 litres/min

OF 30°C (SPECIFIC RATE)

Table 4

FLUE DETAILS

HORIZONTAL FLUE (Side or Rear) mm inches

FLUE DIAMETER 100 3.9
WALL HOLE DIAMETER 110 4.25
WALL HOLE DIAMETER (using internal flue fitting kit) 150 5.9
STANDARD FLUE – MINIMUM LENGTH 127 5.0
STANDARD FLUE – MAXIMUM LENGTH 350 14.0
EXTENDED FLUE – MAXIMUM LENGTH 2500 98.4

Table 2.

4.1 The appliance may be installed in any room although

particular attention is drawn to the requirements of the current
IEE Wiring Regulations BS 7671 and, in Scotland, the electrical
provisions of the Building Regulations applicable in Scotland,
with respect to the installation of appliances in rooms containing
baths or showers.
Where a room sealed appliance is installed in a room containing
a bath or shower, any electrical switch or appliance control using
mains electricity must not be able to be touched by a person
using the bath or shower.

4.2 The appliance is not suitable for external installation.

4.3 The appliance does not require any special wall protection.

4.4 The wall must be capable of supporting the weight of the

appliance. See Table 4.

4.5 The following clearances must be available for installation
and for servicing. See Fig. 2. (note the clearances at the front are
for a removable panel e.g. a door).

4.6 The appliance can be installed in a cupboard used for airing
clothes provided that the requirements of BS 6798 and BS
5440:2 are strictly followed.

Notwithstanding the instructions given in BS 5440:2, this appliance
may be fitted in a compartment with no vents as long as the
minimum clearances stated in Section 6: Air Supply, are maintained.

4.7 The airing space must be separated from the boiler space by
a perforated non-combustible partition. Expanded metal or rigid
wire mesh are acceptable provided that the major dimension is
less than 13mm. See BS 6798:1987.

4.8 No combustible surface must be within 75mm of the casing.
See BS476:4.

4.9 Always consider the possible need to disconnect the pipes
from the appliance after installation.

4.10 LPG Installation: The appliance shall not be installed in a
room or internal space below ground level when it is
intended for use with LPG. This does not preclude the
installation into rooms which are basements with respect to
one side of the building but open to ground level on the
opposite side.

4. Siting The Appliance

5

Above 180mm
In front 0 mm
In front to a fixed surface 600mm
Below 200mm
Right-hand side 10 mm
Left-hand side 10 mm

Fig. 2. Appliance casing dimensions and

required clearances.

Side view

360mm 600mm*

20mm*

200mm* 10mm*

* Space required for installation and servicing

Front view

450mm

10mm*

225mm

180mm

800mm

See Fig. 3.

5.1 The flue must be installed as specified in BS 5440:Part 1.

5.2 The terminal must not cause an obstruction nor the

discharge cause a nuisance.

5.3 If the terminal is fitted within 850mm of a plastic or painted
gutter or within 450mm of painted eaves then an aluminium
shield at least 750mm long should be fitted to the underside of
the gutter or painted surface.

5.4 If a terminal is fitted less than 2 metres above a surface to
which people have access then a guard must be fitted. See
Section 2.9.

5.5 The terminal guard must be evenly spaced about the flue
terminal and fixed to the wall using plated screws.

5.6 In certain weather conditions a terminal may steam and
siting where this could cause a nuisance should be avoided.

5.7 Take care to ensure that combustion products do not enter
ventilated roof voids.

6.1 The appliance does not require a separate vent for
combustion air.

6.2 The appliance can be fitted in a cupboard with no vents for
cooling but the minimum clearances must be increased to those
given below (note the clearances at the front are for a removable
panel e.g. a door).

6.3 If the appliance is to be fitted in a cupboard or compartments
with less clearance than those above (minimum clearances given
in Section 4. Siting The Appliance) then permanent vents for
cooling are required. One at high level and one at low level, either
direct to outside air or to a room. Both vents must pass to the
same room or be on the same wall to the outside air.

6.4 The minimum free areas required are given below.

6.5 Refer to BS 6798 and BS 5440:2 for additional information.

6. Air Supply5. Siting The Flue

6

L

L

K

K

F

F

G

A

M

EJF

HI

D

G

A

B,C

Fig. 3. Siting of the flue terminal.

TERMINAL POSITION MIN. DISTANCE TERMINAL POSITION MIN. DISTANCE

A– directly below an openable window or I– From a terminal facing a terminal 1200mm (47in.)

other opening e.g. air brick. 300mm (12in.) J– From an opening in a car port (e.g. door
B– Below gutters, soil pipes or drain pipes. 75mm (3in.) window) into dwelling. 1200mm (47in.)
C– Below eaves. 25mm (1in.) K– Vertically from a terminal on the same
D– Below balconies or car port roof. 25mm (1in.) wall. 150mm (6in.)
E– From vertical drain pipes and soil pipes. 25mm (1in.) L– Horizontally from a terminal on the same
F– From internal or external corners. 25mm (1in.) wall. 300mm (12in.)
G– Above ground, roof or balcony level. 300mm (12in.) M– From door, window or air vent (achieve
H– From a surface facing a terminal. 600mm (24in.) where possible). 150mm (6in.)

Above the Turret 20mm
In front 250mm
Below 200mm
Right-hand side 75mm
Left-hand side 75mm

POSITION OF AIR FROM AIR DIRECT

AIR VENTS THE ROOM FROM OUTSIDE

HIGH LEVEL 270cm

2

135cm

2

LOW LEVEL 270cm

2

135cm

2

See Figs. 4.

7.1 The system must comply with the requirements of BS 6798
and BS 5449.

7.2 The appliance must not be operated without the system
being full of water, properly vented and pressurised.

7.3 The pressure relief valve operates at 3 bar (45lb/in2). The
discharge must be directed away from electrical components or
where it might be a hazard to the user.

7.4 The pressure gauge indicates the system pressure which
must be maintained.

7.5 The 8 litre expansion vessel is charged to 0.5 bar and is
suitable for a static head of 5 metres (17.5ft). The pressure can be
increased if the static head is greater than 5 metres (17.5ft).

7.6 With an initial system pressure of 0.5 bar, a system capacity
of up to 100 litres can be accommodated. For system capacities
greater than this an extra expansion vessel must be fitted. Refer
to BS 7074 Pt. 1 for more information. The charge pressure can
be increased but with a consequent decrease in system volume.

7.7 The filling point must be at low level. See Fig. 4.

7.8 Water loss must be replaced. See Fig 4. The connection

should be made in the central heating return as close to the
appliance as possible.

7.9 Repeated venting loses water from the system. It is essential
that this water is replaced and the system pressure maintained.

7.10 Connections to the mains water supply must not be made
without the authority of the local Water Company.

7.11 The pump is set at maximum and must not be adjusted.

7.12 Connections in the system must sustain a pressure of up to

3 bar.

7.13 Radiator valves must conform to BS 2767:10.

7.14 Other valves used should conform to the requirements of

BS 1010.

7.15 The appliance is fitted with a fixed internal by-pass. But it is
advisable to keeps one radiator permanently open.

The appliance is

NOT suitable for connection to an open vented

system.

8. Open Vent System

7. Sealed System

7

Fig. 4. Sealed primary water system.

Automatic
air vent

Expansion
vessel

Hot water
out

Water main

Heating
return
Heating
flow

Radiator
valve

Lockshield
valve

Mains cold

water

British Standard
stop valve.
Fixed spindle type

NOTE: A drain cock should be installed at
the lowest point of the heating circuit and
beneath the appliance.

Filling Loop Detail

Heating Return

Non-return

Valve

Non-return

Valve

Test cock

Hose union

Stop cock

Temporary Hose

9.1 The following are general requirements and, if necessary,
reference should be made to the local Water Company before
fitting the appliance.

9.2 MAINS COLD WATER INLET. Devices capable of preventing
the flow of expansion water must not be fitted unless
separate arrangements have been made.
A mini expansion vessel kit is available which contains the
necessary parts for fitting an internal expansion vessel to the
appliance.
See Section 19 COMPONENT PARTS LIST.
A thread sealant compatible with potable water must be
used. An external expansion vessel may be fitted on the
mains cold water connection to the appliance.

9.3

The final 600mm of the mains cold water connection to the

appliance should be made in copper tube only.

9.4 The appliance is suitable for a mains pressure of up to 10 bar
(150 lb/in

2

).

9.5 The appliance is fitted with a mains supply isolating valve.

9.6 The maximum domestic hot water flow rate is 8.0 litres/min

(±15%) (1.8 gallons/min).

9.7 In winter (when the mains inlet water temperature is lower) a
reduced flow rate at the taps may be required to achieve the
type of hot water delivery temperature available in warmer
weather.

9.8 It is suggested that long pipe runs to the taps or shower
should be insulated to prevent the rapid cooling of domestic hot
water after a tap or shower has been turned off.

9.9 Hot and cold taps and mixing valves used with this
appliance must be suitable for operating at mains pressure and
temperatures of 65°C.

9.10 No anti-syphonage arrangements are necessary except for
some loose head showers. See also Section 9.11 following.

9.11 Thermostatically controlled or pressure equalising shower
valves will guard against the flow of water at too high a
temperature.

9.12 The head of a loose head shower must not fall closer than
25mm (1in.) above the top edge of the bath to prevent its
immersion in bath water. Alternatively the shower must be fitted
with an anti-syphonage device at the point of the flexible hose
connections.

9.13 The supply of hot and cold mains water direct to a bidet is
permitted, (subject to local Water Company requirements),
provided that the bidet is of the over-rim flushing type. The
outlet(s) should be shrouded and unable to have any temporary
hand held spray attached. No anti-syphonage arrangements are
necessary.

9.14 LIME SCALE. In temporary hard water areas (more than
350mg/litre or 200ppm calcium bicarbonate) it is
recommended that a proprietary scale reducer is fitted in the
mains cold water connection to the appliance. Consult the
local water company for additional advice.
Installation of a scale inhibitor assembly should be in
accordance with the requirements of the local Water
Company. An isolating valve should be fitted to allow
servicing. The water hardness can be determined by
reference to the local Water Company.

9.15 NOTE: HOT WATER ONLY.
If required the appliance may be used for Hot Water only
before the Central Heating is connected. A 22mm copper by­pass pipe at least 4 meters long must be connected between
the Central Heating Flow and Return, but it is advisable to
connect a small radiator instead.
IT IS NOT RECOMMENDED TO USE THE BOILER IN THIS
CONDITION FOR EXTENDED PERIODS.

9. Hot Water Supply

8

Fig. 5. 230V room thermostat connections.

Fig. 6. 230V programmer connections.

RN RI

X2

Remove link

Neutral

Switched live

Live

RL

CN

Motor

CI

X2

Neutral

Switched live

Live

CL

Remove link

10.1 MAINS SUPPLY.

230 V ~, 50 Hz, 180 watts.
External Fuse: 3A. Internal Fuses: 2AT HRC(F1), and 1.AF (F2).

10.2 It must be possible to completely isolate the appliance.

10.3 The following connection alternatives must be used:

A 3 amp fused three-pin plug and unswitched shuttered socket
outlet (both complying with the requirements of BS 1363) or a
double pole isolator with a contact separation of 3mm in all
poles and supplying the appliance and controls only.

10.4 The appliance must be earthed.

10.5 Mains Cable. 0.75mm2(24 x 0.20mm) to BS 6500 Table 16.

The mains cable must be connected into the terminal

X1,

marked

L (Brown or Red lead), N (Blue or Black lead) and the
earth stud and be held securely in the cable clamp. For access
undo the three bottom screws and remove the facia access cover.
See Fig. 7.

10.6 The wiring between the appliance and the electrical supply
shall comply with current IEE Wiring Regulations and any local
regulations which apply.

10.7 If a room thermostat and/or external programmer is to be
fitted refer to Figs 5 and 6. The devices must be suitable for use
with mains voltage.

10.8 A facia mounted mechanical programmer is available as an
optional extra. Instructions are supplied with the programmer kits.

10.9 A time switch or programmer can be fitted externally to the
appliance.

10.10 The boiler provides automatic frost protection, the use of
a frost thermostat is not recommended. However if an external
frost thermostat is considered necessary then it must be used in

conjunction with a programmer.

Important: To provide external frost protection the appliance
must have the Central Heating Temperature Control Knob set to

supply heating (the appliance may then be left with the central
heating turned off on the programmer).
Connection must be made at

X2 terminals RI and CL. For advice
on external frost thermostats contact Worcester Heat Systems
Technical Helpline

10.11 SAFETY CHECK.

After installation or in the event of an electrical fault the
electrical system shall be checked for short circuits, fuse failure,
incorrect polarity of connections, earth continuity and resistance
to earth.

10. Electrical

9

Fig. 7. Mains electricity connections.

Brown

Strain relief clamp

Blue

Brown

Green/yellow

Green/yellow

Programmer and room thermostat

strain relief clamps

230V

X1

X2

NL

Blue

Fig. 8. Wiring diagram.

Safety

limit
stat

DHW
sensor

CH

sensor

Gas
valve

Pump

Main

Reg

Flow
switch

Air

pressure

switch

Spark

transformer

Mains in

2 pink

2 Blue

2 Red

2 Yellow

2 Orange

Brown

Blue

Blue

Brown

Blue

Brown

Brown

Blue

Link Link

X1

X2

X3

X6

X5 X4

Flame sense
electrode

Spark
electrode

Fan

Brown

White

Green

3 COM

1 NC

2 NO

10

Fig. 9. Functional flow diagram.

F1 2ATHRC

F2 1.25AT

Optional links

SparkFlame sense

Outputs Inputs

Mains
indicator

Modulating

valve

Overheat stat

X6 Pins 8 & 9

X6 Pins 15 & 16

X6 Pins 5,6 & 7

X6 Pins 1 & 2

X6 Pins 19 & 20

X6 Pins 3 & 4

Flow signal

CH temp. sensor

DHW temp. sensor

CH control POT

Air pressure switch

MAINS
PROGRAMMER/CLOCK

FULL SEQUENCE

CONTROLLER

GAS VALVE

LOW VOLTAGE

ELECTRONICS

(Microcontroller)

ROOM STAT

X1

X2

321

1

2

3

4

6

5

RL1

X3

Pin 1 X3 Pin 2

X4 Pin 3

X5 Pin 3

X5 Pin 2X5 Pin 1

X4 Pin 1

FAN

PUMP

RL3

RL4

N

N

N

N

L

Technical Helpline.

The appliance is only suitable for fitting to a sealed system.

11.1 FLUE OPTIONS.

The standard flue length is from 127mm to 350mm measured
from the appliance casing to the outer wall.
Extension flue kits, a vertical take-off adapter, 45° and 90° flue
bends are available to increase the length and redirect the flue as
follows.
Horizontal balanced flue:

a) From 127mm to 2500mm straight flue.
b) From 127mm to 1750mm when a 90° flue bend is

required.

c) From 127mm to 1000mm when two 90° flue bends are

required.
A 90° flue bend is equivalent to 750mm of straight flue. A 45°
flue bend is equivalent to half a 90° bend.
Refer to Figs. 21 and 22 to determine whether extension kits,
90° flue bend, 45° flue bend, or adapters are required.
The maximum number of 90° flue bends allowed is two.

Flue components

1. Turret clamping ring.

2. Flue turret assembly

3. Flue terminal assembly

4. Extension air duct

5. Extension flue duct

6. In-line 90° flue bend

7. In-line 45° flue bend

8. Vertical flue adapter

The flue must be installed as specified in BS 5440 Part 1.

NOTE: READ THIS SECTION FULLY BEFORE COMMENCING
INSTALLATION

11.2 GENERAL FITTING.

Check that the appliance carton contains:- Appliance, Installers
Instruction Pack, Appliance Wall Plate, Users Information Pack,
Installer Hardware Pack and an appliance template.
Check that the position chosen for the appliance is in accordance
with the instructions given in Sections 4 and 5.
Hold the template to the wall. Check that the template is
horizontal. See Fig. 10.
Mark the position of the fixing holes and the position of the flue
hole centre line onto the wall. See Fig. 10.

Side Flue – Extend the flue hole centre line from Fig. 11 along the
appropriate wall. Check that it remains horizontal and mark a
horizontal line. Measure 222mm from the junction of the walls
and mark a vertical line which will then give the position of the
flue hole.
Drill the two fixing holes 60mm deep for No. 12 size plugs. Cut
the flue duct hole at 110mm diameter (150mm dia. for internal
fitting). Ensure that the hole is horizontal through the wall. Fit
the wall mounting bracket.

Drill the two fixing holes 60mm deep for No. 12 size plugs. For
the boiler retaining screws.

Fix the wall plate and check that it is horizontal before tightening
the 2 screws.

Hang the appliance on the wall plate and screw the appliance to
the wall using the screws provided.

11. Installing The Appliance

11

Fig. 10. Appliance mounting plate and flue position.

Fig. 11. Marking out the side flue position.

Mounting wall

Rear flue hole
110mm dia.
(150mm dia. for
internal fixing)

Side flue hole
110mm dia.
(150mm dia. for
internal fixing)

Appliance
casing

Mounting
plate

Fixing holes
(alternatives)

Mounting wall

Mounting
plate

222mm

Side wall

166mm

740mm

400mm

Rear flue position Side flue position

60mm

Appliance
casing

Rear flue hole
110mm dia.
(150mm dia. for
internal fixing)

Mounting wall

Side wall

222mm

166mm

Connect the gas, water and pressure relief valve connections to
the appliance. The primary system should be flushed and
treated in accordance with the recommendations of
BS7593:1992.

If the air and flue duct assembly is to be fitted from inside the
room then the ducts must be adjusted to length, assembled and
inserted through the wall at this stage before fitting the flue
turret to the appliance. Refer to Section 11.3 following for the
assembly of the air and flue ducts.

Remove the fan. See Section 14.3(e).

11.3 AIR AND FLUE DUCT PREPARATION AND ASSEMBLY

Check the contents of the standard flue kit against the packing
list. Similarly check the extension kits if applicable.
Remove all the packing from the flue and terminal assembly.
The standard flue kit accommodates a flue assembly up to
350mm long measured from the appliance casing to the outer
wall face. See dimension

L, Figs.13 and 14.

When dimension

L is greater than 350mm extension flue
assemblies will be required.
It will not be necessary to cut either the ducts attached to the
turret or the terminal unless

L = 350 to 450mm.

Measure and cut the extension ducts to length ensuring that the
cuts are square and free from burrs. Always check the
dimensions before cutting the ducts.
All extension duct dimensions refer to the straight lengths. The
socketed ends must not be removed or included in any
measurement.

11.4 EXTERNAL FITTING OF THE DUCT ASSEMBLY

Measure distance L.
Side flue duct length =

L + 184mm. See Fig. 14.

Rear flue duct length =

L + 181mm. See Fig. 13.
Do not cut either the turret or the terminal assembly ducts
unless

L = 350 to 450mm.

1. Should L = 350 to 450mm then cut the terminal assembly

ducts reducing the length of the ducts to 200mm. Then cut each
extension duct to 200mm (See Fig. 15). Assemble the flue as
described below ensuring the correct length (

L+184mm for side

flues or

L+181mm for rear flues).

12

Fig. 13. Rear flue.

Fig. 14. Side flue.

Fig. 15. 350-450 Special.

Rear face of appliance
and face of mounting
wall

External
wall face

40mm

Make
good

L

Appliance casing

Fixing screws

Flue extension
duct length
200mm

Air
extension
duct
length
200mm

Terminal assembly
reduced to 200mm

Turret assembly
with full
standard
duct
lengths

Rear flue

L + 181mm

Side flue L + 184mm

L = 350mm-450mm

Appliance side panel

External
wall face

40mm

Make
good

L

Fig. 12. Appliance pipework connections.

(A)

100mm

36.5mm

(B)

(C)

(D)

(E)

(F)

A Safety Relief = 50mm
B CH Flow = 95mm
C DHW Out = 160mm
D Gas Inlet = 225mm
E Mains Cold Water In = 290mm
F CH Return = 355mm

2. If L is within the range 127mm to 350mm then the flue can
be telescopically adjusted to the correct length (

L+184mm for

side flues or

L+181mm for rear flues). The ducts are then fixed
by drilling a pilot hole through the hole in the air duct and screwing
the self tapping screw provided into the two ducts (See Fig. 16).

3. If L is within any of the following ranges it will not be
necessary to cut the extension ducts:

0.88m to 1.10m, 1.63m to 1.85m or 2.38m to 2.50m.
Each extension must be connected to the first section of flue or
the previous extension by firstly fitting the inner flue ducts
together and pilot drilling and fixing. (See Fig. 17). Then the outer
air ducts can be similarly fixed using the pair of screws provided.
The flue terminal section can then be telescopically adjusted and
fixed as before (See Fig. 16) ensuring the correct length
(

L+184mm for side flues or L+181mm for rear flues).

4. In the event of L not falling within any of the above ranges

it will be necessary to cut the FIRST extension length. The air
and flue duct lengths should both be reduced to the same

length: L – 240mm where one extension is used; L – 990mm with
two extensions and

L – 1,740mm with three. (See Fig. 17). The flue
can then be assembled ensuring that the cut extension is fitted to
the turret duct assembly first and that the flue is adjusted to the
correct length of (

L+184mm for side flues or

L+181mm for rear flues) (See Fig. 16).

5. Finishing the flue

Apply the plastic tape provided to the last section of flue where it
will be sealed to the external brickwork.
From inside, push the assembly through the wall, align the flue
turret with the socket on the appliance, push the turret down to fully
engage it and clamp in place with the turret clamping ring. See Fig.

18.
Make good the internal and external brickwork or rendering.
Refit the fan and replace the inner casing cover.

13

Fig. 17. Extensions.

Fig. 18. Flue turret fixing.

Reset button

Flue Gas

Test Point

Flue turret

Turret clamping

ring

Rear flue L + 181mm

Side flue L + 184mm

Appliance casing

Fixing screws Fixing screw

Turret
assembly

Terminal
assembly

L = 450mm-2500mm

Extensions of equal length

Shorten first extension fitted

to the turret assembly

Fig. 16. Standard flue assembly.

Appliance casing

Fixing screw

Turret
assembly

Terminal
assembly

Rear flue

L + 181mm

Side flue L + 184mm

L

11.5 INTERNAL FITTING OF THE DUCT ASSEMBLY

The rubber sealing gasket and the clamping ring are available from
Worcester Heat Systems.
Measure and cut the ducts as previously described for external
fitting (Section 11.4). Fix the ducts to the terminal and fit the rubber
sealing gasket and clamp to the terminal. Centralise the gasket and
tighten the clamping ring. See Fig. 19. Slide the flue centering ring
onto the air duct and tighten the screw. See Fig. 20. Fix the ducts
and terminal assembly to the flue turret as described in Section 11.4
preceding.

Apply the plastic tape provided to the last section of flue where it
will be sealed to the external brickwork.
Push the assembly through the wall so that the gasket flange is
against the outside face of the wall. See Fig. 20.

Align the flue turret with the socket on the appliance, push the
turret down to fully engage it and clamp in place with the turret
clamping ring. See Fig. 18.
Refit the fan and replace the inner casing cover.
Seal the gap around the duct with the flexible seal provided and
make good. See Fig. 20.

11.6 FLUE BENDS

See Figs 21 and 22.
Measure distances

X, Y and Z as appropriate.

Side flue duct length =

X + 63mm. See Fig. 21.

Rear flue duct length =

X + 60mm. See Fig. 21.
Cut the flue and air ducts which are to make up the first section
X such that both the assemblies are of equal length (either X +
63mm or

X + 60mm). Extensions will be necessary to allow X to
be larger than 250mm.
Any extension ducts are fixed by drilling a pilot hole through the
hole in the duct or elbow and screwing the self tapping screw

provided into the two ducts. (See Fig. 21).
The length

Y is the distance between bends the ducts must be

cut to

Y – 162mm. The swaged ends must be removed from the
extension tube and only the air duct needs fixing. See Fig. 21.
Z is the final flue length from the last elbow to the outside face of
the external wall. The first duct sections fitted to the elbow must
have unswaged ends. The length of the air ducts should be

Z –
196mm. The inner flue duct must be 30mm longer than the air
duct. If

Z – 196mm is less than 160mm then the terminal section
will need to be shortened to the same length as the extension flue
section fitted to the elbow (length

Z – 100). If flue extensions are
needed to attain the required length care must be taken to ensure
that the last section of flue is longer than 260mm.
Each extension must be connected to the previous section of flue
or bend by firstly fitting the inner flue ducts together and pilot
drilling and fixing as above (See Fig. 21). Then the outer air ducts
can be similarly fixed using the pair of screws provided. The flue
terminal section can then be telescopically adjusted and fixed as
before (See Fig. 21), ensuring the correct length of

Z – 41.
The silicon sealant supplied should be applied to the flue ducts
which engage into elbows. See Fig. 21.
From inside, push the assembly through the wall
Align the flue turret with the socket on the appliance, push the
turret down to fully engage it and clamp in place with the turret
clamping ring. See Fig. 18.
Make good the internal and external brickwork or rendering.
Refit the fan. Do not use any sealant on the joint. Replace the
inner casing cover.

14

Fig. 21. Flue bends.

56mm

Z Ð 41mm

56mm

Side flue

X + 63mm

Rear flue X + 60mm

Z

Y

X

Y

Ð 162mm

Fig. 19. Terminal assembly for internal

fitting of the flue.

Flue centring ring Flue terminal

Flue duct

Rubber
sealing
gasket

Air duct

Rubber sealing
gasket

Clamping ring

Flue terminal

Fig. 20. Duct and terminal assembly for

internal fitting of the flue.

11.7 VERTICAL ADAPTER

Measure and fit the flue as in Section 11.6 Flue bends except the
first section length is measured from the case top and the ducts
are cut to

X – 168mm. The minimum length for X is 190mm. See

Fig. 22.

11.8 FINAL INSTALLATION

Check that all the water and gas connections have been
tightened.
If a facia mounted programmer is to be fitted follow instructions
with the programmer..
Remove the facia bottom panel as described in Section 14.3(c).
Connect the mains electrical supply to the appliance at terminal
X1. See Fig. 23. Connect any room and/or frost thermostats. The
electrical leads must pass through the appropriate space in the
control panel and be fixed with the cable clamps provided. Refit
the facia panel.
Test the gas supply pipework up to the appliance for soundness
as indicated in BS 6891.
Refer to Section 12 for a full description of the filling, venting and
the pressurising of the system.
If the appliance is not to be commissioned immediately, replace
the cabinet front panel. Check that the gas supply, the electrical
supply and the water connections are all turned off.
If the premises are to be left unoccupied during frosty conditions,
then drain the appliance and system. For short inoperative
periods, leave the appliance under the control of the built in frost
thermostat or the remote frost thermostat (if fitted) or leave
operating continuously with the room thermostat set at 6°C.

15

Fig. 22. Vertical adaptor with

horizontal flue.

X-168

Y-162

90¡

90¡

Appliance

Vertical flue adaptor required
for upwards section

TOTAL STRAIGHT FLUE LENGTH
X + Y + Z or X + Z

2500mm with one bend
1750mm with two bends
1000mm with three bends

Z-41

Fig. 23. Mains electricity connections.

Brown

Strain relief clamp

Green/yellow

Programmer and room thermostat

strain relief clamps

230V

X1

X2

NL

Blue

12.1 SUMMARY

The appliance is dispatched with the controls set to provide a
maximum output for domestic hot water and central heating of

23.4 kW (80,000 Btu/h). The appliance automatically modulates
to satisfy lower heat loads.
Domestic Hot Water and Central Heating Systems. Check that
both the mains water supply and central heating systems have
been fully flushed out at installation.
Gas Service. The complete system, including the meter, must be
inspected and tested for soundness and purged as indicated in
BS 6891.

12.2 APPLIANCE AND CENTRAL HEATING
SYSTEM PREPARATION

Remove the cabinet front panel.
Check that the electrical supply and the gas service to the
appliance are off.
Check that all the water connections throughout the system are
tight.
Open the system valves at the appliance. Open all the radiator
valves, fill the system and vent each radiator in turn.
Remove the inner casing cover as described in section 14.3(b).
See Fig 24.

The automatic air vent will vent the appliance. Check that the air
vent cap has been removed. See Fig. 25.
Check that the pressure relief valve operates by turning the knob
anti-clockwise until it releases. Water should be expelled from
the discharge pipe. See Fig. 26. Lower the control box to gain
access. Refer to Section 14.3(c).

Set the Expansion Vessel Pressure

The charge pressure of the expansion vessel as dispatched is 0.5 bar,
which is equivalent to a static head of 5 metres (17ft). The charge
pressure must not be less than the static head at the point of
connection. A Schraider type tyre valve is fitted to the expansion
vessel to allow the charge pressure to be increased if necessary.

Set the System Pressure

Fill the system until the pressure gauge shows 2.5 bar (37
lb/ins

2

) and check for water soundness. Release water from the
system using the relief valve test knob until the initial System
Design Pressure is obtained, up to a maximum of 1.5 bar.
Initial System Design Pressure (bar) = Expansion Vessel Charge
Pressure +0.3 (bar).

Note: 1 bar is equivalent to 10.2 metres (33.5 ft) of water.
Set the movable pointer on the pressure gauge to coincide with
the indicating pointer giving a permanent record of the set
system pressure.
If the pressure indicated on the pressure gauge is greater than

2.6 bar when operating at the maximum central heating
temperature, an extra expansion vessel must be fitted to the
system as close as possible to the appliance central heating
return connection.
The appliance (as dispatched) can accommodate a system
volume of about 100 litres. Refer to BS 7074 Part 1. If the system
volume is in excess of that accommodated by the expansion
vessel fitted to the appliance then an extra vessel must be fitted
as close as possible to the central heating return connection of
the appliance.
Any extra vessel fitted must be pressurised to the same figure as
the integral vessel. If the expansion vessel fails then the specified
replacement must be fitted.

12. Commissioning The Appliance

16

Fig. 25. Appliance components and fixings
(upper assembly).

Flue hood

Overheat
thermostat

Burner fixing
screws (2)

Combustion
chamber
cover fixing
clips (2)

Auto air
vent

Fan assembly
fixing screws (4)

Flue Gas
Test Point

Fig. 24. Appliance casing and control
equipment fixings.

Inner casing
cover
screws (4)

Side casing
fixing
screws (4)

Facia panel
fixing
screws (2)

Bottom facia
panel fixing
screws (3)

Fig. 26. Pressure relief valve.

Pressure relief
valve.
(Turn knob
anti-clockwise
to test).

12.3 PROGRAMMER

Any programmer fitted on the appliance should be set up at this
stage following the instructions sent with the programmer.

12.4 APPLIANCE OPERATION

Turn off the gas and electricity supplies to the appliance.
Undo the two screws and hinge down the facia.
Loosen the burner pressure test point screw and connect a
pressure gauge. See Fig. 27.

Domestic Hot Water.

Set any Programmer to HEATING & WATER.
Turn on the gas and electricity supplies.
Set the Central Heating temperature control knob to Off.
A tap should be opened to create a hot water demand then a
continuous ignition spark will occur until the burner is alight and
sensed by the control circuit. The burner will light and remain at
its maximum setting. The burner pressure should be between

13.4 and 13.8 mbar on Natural gas (33.0 and 35.0 mbar on
Propane). If the burner pressure is low, check that the supply
pressure at the gas valve inlet is at least 19 mbar for Natural gas
(37 mbar for Propane).
Test for gas soundness at the joint between the burner and the
gas valve with leak detection fluid.
Note: The burner pressure is factory set and if (after checking
that the supply pressure is sufficient) the correct pressure is not
obtained then Worcester Heat Systems Service Department
should be contacted.
Gradually close the hot tap and check that the burner pressure
drops. Fully open the tap and check that the burner pressure
rises. Fully close the tap and check that the burner goes off. The
fan may continue running until the appliance has cooled.

Central Heating

Check that all the radiator valves are open.
Check that the system is pressurised and set to the required
pressure as indicated on the gauge.
Set any Programmer to HEATING & WATER.
Turn on the gas and electricity supplies.
Set the room thermostat and the Central Heating Temperature
Control to maximum.
The burner will light.
The appliance will modulate its output between 7.5 and 23.4 kW
over a period of about twenty minutes.
Check the system to ensure that all the radiators are heating up
evenly.
Shut down all but one of the radiators and observe the burner
pressure fall. Open all of the radiator valves and check that the
burner pressure rises.
Balance the system so that the required temperature difference
across the central heating flow and return pipes is obtained. See
Table 3, Section 3 Data Tables.
Set the room thermostat to minimum and check that the burner
goes out. Reset the room thermostat to maximum and the
burner will re-light after a short anti-cycle delay and follow the
normal operating procedure.
Check for proper ignition of the burner after a break in the gas
supply. Turn off the gas service cock and wait for 60 seconds. The
burner will go out but sparking from the electrode will continue
for 10 seconds when the appliance will enter a “lockout” state.
Carefully open the gas service cock, interrupt the mains power
supply to the appliance for a few seconds to reset the controls
and observe the burner re-light and follow the normal sequence
of operation.
Turn off the gas service cock and the electrical supply to the
appliance.
Drain the system while the appliance is still hot.
Refill, vent and re-pressurise as described in Section 12.2.

Domestic Hot Water and Central Heating

Turn on the electricity supply to the appliance and open the gas
supply cock at the appliance.
Set the Central Heating temperature control knob to demand
and any programmer to HEATING & WATER. If a programmer is
fitted, set the domestic hot water to Continuous or 24 Hrs and
the central heating to ON. The burner will light and heat will pass
into the system. Turn on a hot water tap and check that after a
short delay fully heated hot water is discharged from the tap.
Close the tap and the burner will go off. After a short time the
appliance will then return to the central heating mode and
automatically balance with the system requirements.
Set the Central Heating Temperature Control Knob to OFF and the
burner will go out.

12.5 COMPLETION OF COMMISSIONING

Disconnect the pressure gauge and tighten the test point screw.
Restart the appliance and check for gas soundness around the
test point screw.
Refit the cabinet front panel.
If the appliance is being passed over to the user immediately,
refer to Section 13 - Instructions to the User and set the controls
to the users requirements.
If the appliance is to be left inoperative, check that the Central
Heating Temperature Control is set to OFF. Turn off the gas service
cock and switch off the electricity supply.
If there is any possibility of the appliance and system being left
inoperative during frosty conditions, drain the appliance and
system. If the premises are to be left unoccupied during frosty
conditions, then drain the appliance and system. For short
inoperative periods, leave the appliance under the control of the
built in frost thermostat or the remote frost thermostat (if fitted)
or leave operating continuously with the room thermostat set at
6°C.

17

Fig. 27. Gas valve.

Main gas valve
connections
(Black : blue : brown :
green/yellow)

Burner pressure
test point

Inlet pressure test
point

Electrical connections Ð
modulator (Blue : Blue)

Modulating
solenoid

Minimum
pressure
adjuster

Maximum pressure
adjuster
Note: Clockwise to
increase and anti­clockwise to
decrease the
pressure

13.1 Tell the user how to operate the appliance and hand over
the Users Instructions leaflet.

13.2 Tell the user what to do if the heating system is not to be
used in frosty weather.

13.3 Tell the user the sealed system set pressure.

13.4 Tell the user of the importance of regular servicing.

Worcester Heat Systems Ltd. offer a comprehensive maintenance
contract.

13.5 Set the system controls to the user’s requirements.

13.6 If an external programmer has been fitted which has a

programmable domestic hot water facility then it is suggested
that this be set to Continuous or the equivalent.

14.1 SERVICING

To ensure continued efficient operation of the appliance it must
be checked and serviced as necessary at regular intervals. The
frequency of servicing will depend upon the particular
installation conditions and usage, but once per year should
generally be adequate. The extent of the service required by the
appliance is determined by the operating condition of the
appliance when tested by fully qualified engineers.
Any service work must be carried out by competent engineers
such as British Gas or Corgi registered personnel.

14.2 PRE-SERVICE INSPECTION

Check that the flue terminal and the terminal guard, (if fitted), are
clear.
If the appliance is in a compartment, check that the ventilation
openings in the compartment door or walls are clear. See Section
6 - Air Supply.
Check the system and remake any joints or fittings which show
signs of leakage.
Refill, vent and re-pressurise as described in Section 12.2.
Operate the appliance and the system taking note of any faults.

Measurement of the Flue Gases

For consistency of results of the flue gas measurements it is
necessary to have a constant output and for the appliance to be
at equilibrium.
Turn on a tap to create a hot water demand.
Wait until the appliance reaches thermal equilibrium (approx. 10
minutes).
Remove the test point sealing screw on the appliance top panel.
See Fig. 30.
Connect to the test point with a piece of tubing.
Expected measurements should be between:

For Natural Gas:

For Propane:

When calculating the equivalent flue length a flue bend is
equivalent to 750mm of straight flue.
After taking the measurement replace and tighten the sealing
screw.

IMPORTANT

Disconnect the electrical supply at the mains and turn off the
gas supply at the gas service cock on the appliance before
servicing.
After completing the service always test for gas soundness as
indicated in BS 6891.

14. Inspection And Service13. Instructions To The User

18

Equivalent flue Carbon Carbon
length (metres) Dioxide (%) Monoxide (%)

0.5 6.9 0.0008

1.0 7.0 0.0009

1.5 7.1 0.0010

2.0 7.3 0.0012

2.5 7.4 0.0013

Equivalent flue Carbon Carbon
length (metres) Dioxide (%) Monoxide (%)

0.5 7.9 0.0017

1.0 8.0 0.0020

1.5 8.2 0.0024

2.0 8.5 0.0030

2.5 8.8 0.0035

Fig. 28. User controls.

Reset button

Mains indicator

C.H. temperature control
and on/off knob

System
pressure
gauge

14.3 DISMANTLE THE APPLIANCE

To carry out a full and comprehensive service of the appliance
remove the following parts to gain access to the components
which need to be checked or serviced.

(a) Cabinet Front Panel. Remove by lifting off the supports.
(b) Inner Casing Cover. Check that the electricity supply to the

appliance is turned off. Remove the cabinet front panel. Unscrew
the four screws securing the cover to the casing and lift off. See
Fig. 29.
(c) Facia Panel. Check that the electricity supply to the appliance
is turned off. Remove the cabinet front panel. Unscrew the two
upper screws as shown in Fig. 29. and hinge down the facia
taking care not to damage the pressure gauge capillary tube or
electrical connections.

(d) Bottom panel. Unclip and remove the appliance bottom
panel.
(e) Fan. Remove the inner casing cover. Carefully unplug the
electrical connections and pull off the sensing tubes. Unscrew
the four fixing screws and remove the fan assembly. See Fig. 30.
(f) Combustion Chamber Front. Remove the inner casing cover.
Undo the spring clips fixing the combustion chamber front. See
Fig. 30.
(g) Flue Hood Assembly. Remove the fan assembly. Remove the
combustion chamber front. Lift and slide the flue hood assembly
from the appliance. See Fig. 30. When refitting the hood ensure
that the rear return edge passes under the lip at the rear of the
combustion chamber.
(h) Burner Assembly. Remove the combustion chamber front.
Pull off the two spark electrode leads and disconnect the flame
sense lead. Undo the burner fixing screws. Lift up and remove
the burner assembly from the appliance. See Fig. 31.

14.4 SERVICE OF COMPONENTS
Clean the Fan.

Any dust or fluff should be removed with a soft
brush or by blowing. Take care not to distort the pressure
sensing device.
Clean the Main Burner. Brush the blade tops and mixing tube
with a soft brush and check that all the flame ports are clear.
Remove any blockages with a non-metallic brush. Inspect the
injector and clean with a soft brush. Replace the injector if it
appears damaged. Do not use a wire brush or anything likely to
cause damage. Replace the spark and sense electrodes if they
appear damaged.
Clean the Gas to Water Heat Exchanger. Clean the heat
exchanger using a soft brush. Remove the deposits from the
bottom of the combustion chamber. Do not distort any of the
blades.
Combustion Chamber Insulation. Examine and replace any
pads that are damaged. Remove any dust or deposits using a
soft brush.
Reassemble the appliance in the reverse order.
Check that all components are in place and correctly fixed. Leave
the cabinet front panel to be fitted after checking the operation
of the appliance.

14.5 TEST THE APPLIANCE

On completion of the service and reassembly of the appliance,
check for gas soundness and the correct operation of the
appliance as described in Section 12 - Commissioning.
Refit the cabinet front panel and reset the controls to the users
requirements.

19

Fig. 31. Burner and electrode assembly.

Spark electrode

Injector

Fig. 30. Appliance components and fixings
(upper assembly).

Flue hood

Overheat
thermostat

Burner fixing
screws (2)

Combustion
chamber
cover fixing
clips (2)

Auto air
vent

Fan assembly
fixing screws (4)

Flue Gas
Test Point

Fig. 29. Appliance casing and control
equipment fixings.

Inner casing
cover
screws (4)

Side casing
fixing
screws (4)

Facia panel
fixing
screws (2)

Bottom facia
panel fixing
screws (3)

15.1 IMPORTANT

Switch off the electricity and gas supplies before replacing any
components. After the replacement of any components, check
for gas soundness where relevant and carry out functional
checks as described in Section 12 - Commissioning

15.2 COMPONENT ACCESS

To replace components it is necessary to remove one or more
sections of the cabinet and cover plates within the appliance as
described in Section 14.3. The facia panel may also need to be
hinged down as described in Section 14.3 (c).

15.3 DRAINING THE APPLIANCE

Check that the electricity supply to the appliance is turned off.
Before removing any component holding water it is important
that as much water as possible is removed from the appliance.
(a) Central Heating Circuit. Turn off the central heating flow and
return valves at the appliance. Open the pressure relief valve,
make sure that the dust cap on the auto air vent is removed. See
Fig. 30. Close the pressure relief valve when the flow has
stopped. Some water will remain in the expansion vessel, pump
and Gas to Water heat exchangers and extra care must be taken
when removing these components.
(b) Domestic Hot Water Circuit. Turn off the mains cold supply
valve at the appliance and open the lowest hot water tap. A
quantity of water will remain in the Gas to Water heat exchanger,
extra care must be taken when removing this component.

15.4 COMPONENT REPLACEMENT

1. Automatic Air Vent.

See Figs. 30. and 32.
Remove the inner casing cover as described in Section 14.3 (b).
Drain the central heating circuit as described in Section 15.3 (a).
Unscrew air vent from the heat exchanger.
Fit the replacement assembly ensuring thread sealant is applied
and the dust cap is removed.
Open the valves and fill and re-pressurise the system as
described in Section 12.2.

2. Air Pressure Switch. See Fig. 34.
Check that the electricity supply to the appliance is turned off.
Remove the cabinet front panel as described in Section 14.3 (a)
and lower the facia. Section 14.3(c).
Carefully pull off the sensing tubes and the electrical connections
from the switch. Remember to note their positions.
Unscrew the two screws behind the Air Pressure Switch and
remove the switch from the appliance.
Fit the replacement switch in the reverse order ensuring that the
electrical connections have been made to the correct terminals
on the switch. Check that the sensing tubes are fitted correctly.

3. Fan. See Fig. 30.
Check that the electricity supply to the appliance is turned off.
Remove the fan assembly as described in Section 14.3(e).
Fit the replacement fan in the reverse order.

4. Overheat Thermostat. See Fig. 30 and 32.
Check that the electricity supply to the appliance is turned off.
Remove the inner casing cover as described in Section 14.3 (b).
Carefully pull off the two wires from the thermostat head.
Undo the retaining nut on the top of the appliance and remove
the retaining clip from the heat exchanger. Carefully withdraw
the thermostat from the appliance.
Fit the replacement thermostat in the reverse order ensuring that
some heat sink compound is between the thermostat and the
heat exchanger.

5. Gas to Water Heat Exchanger.See Fig. 32.
Check that the electricity supply to the appliance is turned off.
Drain the central heating circuit and domestic circuits as
described in Section 15.3 (a) and (b).
Remove the inner casing cover, fan, flue hood assembly,
combustion chamber front, overheat thermostat, automatic air
vent and combustion chamber side insulation as described in
Sections 14.3 (b, e, f and g), 15.4 (1) and 15.4 (4).
Fit the replacement heat exchanger in the reverse order ensuring
that all the fibre washers are correctly fitted and a layer of heat
sink compound is on the thermostat.
Open the valves and fill and re-pressurise the system as
described in Section 12.2.

15. Replacement Of Parts

20

Fig. 32. Combustion chamber.

Heat
exchanger

Overheat
Thermostat

Hot water heat
exchanger
connections

Cut-outs in
combustion
chamber sides

Pump bulk
head
connector

Central heating
heat exchanger
connections

Auto air
vent

6. Combustion Chamber Insulation.

Check that the electricity supply to the appliance is turned off.
Drain the central heating circuit as described in Section 15.3(a).
Remove the inner casing cover, fan, flue hood assembly, burner,
and Gas to Water heat exchanger as described in Sections 14.3
(b, e and f), and 15.4 (5). Remove the fibre insulation pads from
the combustion chamber side, rear, and front sections.
Fit the replacement pads in the reverse order taking care not to
damage them.
Open the valves and fill and re-pressurise the system as
described in Section 12.2.

7. Burner. See Fig. 31.
Check that the electricity and gas supplies to the appliance are
turned off.
Remove the burner assembly as described in Section 14.3 (h).
Fit the replacement burner in the reverse order taking care not to
damage the electrode leads.

8. Burner Injector. See Fig. 31.
Remove the burner as described in Section 14.3 (h).
Unscrew the brass injector from the manifold.
Fit the replacement injector in the reverse order.

9. Spark Electrode Assembly. See Fig. 31a.
Remove the combustion chamber front as described in 14.3 (g)
Carefully pull off the two electrode leads,
Undo the M4 extended nut and remove the spark electrode
assembly from the burner.
Fit the replacement electrode in the reverse order, checking that
the spark gap is 3.5 to 4.5mm.

10. Flame Sensor. See Fig. 31.
Remove the burner as described in sections 14.3(h) and 15.4(8).
Undo the M3 screw and remove the sense electrode from the
burner.
Fit the replacement electrode in the reverse order, checking that
the sense gap is 5 to 6mm.

11. Gas Valve. See Figs. 33. and 34.
Check that the electricity and gas supplies to the appliance are
turned off.
Hinge down the control box assembly in the servicing position
as described in Section 14.3(d).
Whilst supporting the valve unscrew the plug retaining screw
and carefully pull off the electrical solenoid plug connection and
the two modureg leads.
Undo the 8 manifold screws and remove the gas valve. See Fig. 34.
Fit the replacement gas valve in the reverse order ensuring the
“O” rings are correctly fitted.
Turn on the gas supply and check for soundness.
To set the burner pressure. See Fig. 33.
The minimum and maximum burner pressures must be set after
a new gas control has been fitted.
The maximum burner pressure must be set first, as any
adjustment of the maximum pressure influences the minimum
pressure setting.
Start the appliance in the domestic hot water mode as described
in section 12.4. - Appliance Operation.
Adjust the maximum pressure adjustment screw on the gas
valve to give a burner pressure of 13.6 mbar on natural gas, for
propane the maximum pressure adjustment must be increased
to maximum clockwise, this should give 33.0 - 35.0 mbar.
End the demand and reset the appliance by interrupting the
mains electricity supply. (Otherwise there is a four minute anti­cycle delay at the end of a demand).

Restart the appliance in central heating mode and adjust the
minimum adjustment screw on the gas valve to give a pressure
of 1.0 mbar on natural gas or 3.5 mbar on propane. See Fig. 33.
After completing the adjustments, check the minimum and
maximum pressures and re-adjust as necessary. Once this has
been done the clear cap should be re-fitted to the adjuster and
the retaining screw tightened. Coat the screw with paint or nail
varnish to prevent user adjustment.

12. Central Heating Sensor. See Fig. 34.
Check that the electricity supply to the appliance is turned off.
Hinge the facia assembly in the servicing position as described in
Section 14.3(c and d).
Carefully pull off the two leads from the sensor.
Pull off the sensor and spring retaining clip from the pipe.
Fit the replacement sensor in reverse order with a layer of heat
sink compound between the faces. Refit the leads.

21

Fig. 34. Gas valve pump and air pressure

switch.

Lower pump
connection

Gas valve
electrical
connections

Pressure gauge
connection

Central Heating
Sensor

Air pressure
switch

Air pressure switch

connecting tubes

PumpGas

valve

Top gas valve

connection (4 bolts)

Red
pipe

Fig. 27. Gas valve.

Main gas valve
connections
(Black : blue : brown :
green/yellow)

Burner pressure
test point

Inlet pressure test
point

Electrical connections Ð
modulator (Blue : Blue)

Modulating
solenoid

Minimum
pressure
adjuster

Maximum pressure
adjuster
Note: Clockwise to
increase and anti­clockwise to
decrease the
pressure

Fig. 31a. Spark electrode assembly.

3.5-4.5mm

2.5-5mm

13. Domestic Hot Water Sensor.

Check that the electricity supply to the appliance is turned off.
Hinge the facia assembly in the servicing position as described in
Section 14.3(c and d).
Carefully pull off the two leads from the sensor.
Undo and remove the clamping screw.
Pull off the sensor and spring retaining clip from the pipe.
Fit the replacement sensor in the reverse order ensuring a layer
of heat sink compound is between the faces. Refit the leads.

14. Circulating Pump. See Figs. 32 and 34.
Check that the electricity supply to the appliance is turned off.
Drain the central heating circuit as described in Section 15.3(a).
Hinge the facia assembly in the servicing position as described in
Section 14.3(c).
Undo the two union nuts and the pipe to the expansion vessel,
remove the pump from the pipe-work. Support the pump and
remove the electrical cover.
Disconnect the electrical wires taking note of their positions.
Fit the replacement pump in the reverse order using new sealing
washers.
(Alternatively replace the pump head only by removing the four
Allen screws on the pump, remove the head and support whilst
removing the electrical connections. Refit the new head).
Open the valves and fill and re-pressurise the system as
described in Section 12.2
Note: The direction of flow should be upwards. The speed should
always be set to maximum.

15. Expansion Vessel.

Drain the central heating circuit as described in Section 15.3(a).
Isolate the gas supply at the mains.
Then either fit a separate expansion vessel on the central heating
return to the appliance or replace the existing vessel as
described below.
Drain the domestic circuit as described in Section 15.3(b).
Disconnect the flue system at the boiler.
Disconnect the appliance pipework at the appliance entry points
ensuring precautions are taken to cope with any water
remaining in the appliance.
Remove the appliance from the wall.
Disconnect the expansion vessel from the appliance by undoing
the fitting nut at it’s base.
Fit the replacement vessel in the reverse order.
Open the valves and fill and re-pressurise the system as
described in Section 12.2

16. Pressure Relief Valve. See Fig. 35.
Drain the central heating circuit as described in Section 15.3(a).
Hinge down the facia assembly as described in Section 14.3(c)
Remove the Bottom panel as described in Section 14.3(d)
Undo the discharge pipe connection and remove the valve
retaining clip. Remove the valve taking care not to distort the
pipework.
Fit the replacement valve in reverse order. Reconnect the
discharge pipe.
Open the valves and fill and re-pressurise the system as
described in Section 12.2

17. Water Flow Switch. See Fig. 36.
Check that the electricity supply to the appliance is turned off.
Drain the domestic hot water circuit as described in Section

15.3(b).
Remove the two upper screws and hinge down the facia panel as
described in Section 14.3(c).
Undo the two union nuts securing the “T” piece and remove the
housing from the pipework.
Disconnect the electrical connection.
Fit the replacement water flow switch in the reverse order
ensuring new fibre washers are fitted to the new switch body.

18. Domestic Hot Water Flow Restrictor. See Fig. 36.
Remove the water flow switch as described in Section 15.4-17.
Undo the two union nuts securing the “T” piece and remove the
housing from the pipework.
The plastic flow restrictor is located within the “T” piece on the
water flow switch.
Fit the replacement flow restrictor and reassemble in the reverse
order ensuring the fibre washers are in place.

19. Pressure Gauge.

Check that the electricity supply to the appliance is turned off.
Drain the central heating circuit as described in Section 15.3(a).
Remove the two upper screws and hinge down the facia panel as
described in Section 14.3(c).
Prize back the retaining clips securing the gauge to the facia
panel remove wire clip and unplug the gauge from the pump
inlet pipe.
Fit the replacement gauge in the reverse order ensuring the “O”
ring is in place.
Open the valves and fill and re-pressurise the system as
described in Section 12.2

22

Fig. 35. Pressure relief valve.

Pressure relief
valve.
(Turn knob
anti-clockwise
to test).

Fig. 36. Water Flow Switch. (Side View)

Flow Restrictor

Water Flow Switch

ÒTÓ Piece

20. Control Board.

Check that the electricity supply to the appliance is turned off.
Undo the 3 screws and remove the facia bottom panel.
Remove the two upper screws and hinge down the facia
assembly.
Carefully pull off all the connectors. Disconnect the mains supply
lead at terminal

X1 and the earth connection at the back.
Remove the four corner screws on the back of the facia and
separate the metal back panel from the plastic facia.
Remove and retain the brass nut and washer.
Release the six pillars on the control board and pull the control
board forward off the back panel.
Fit the replacement board in the reverse order ensuring it is
pushed firmly onto the six pillars and clicks into place. Special
care should be taken with the brass post and nut to ensure a
good earth contact. (Check earth continuity between the
incoming earth and the appliance chassis).
Refit the facia panel and hinge the control box assembly in the
servicing position as described in Section 14.3 (c).

21. Gauze filter. See Fig. 37.
Remove the water flow switch as described in section 15.4-17.
Undo the lower union nut on flow switch housing.
Undo the nut on the isolating valve and remove the mains water
inlet pipe. Carefully extract the filter from the valve end of the
pipe.
Replace the filter and refit the pipe in reverse order.

22. Flue flow sensor. See Fig. 38.
Check that the electricity supply to the appliance is turned off.
Remove the fan assembly as described in Section 14.3(e).
Unscrew the single central retaining screw and withdraw the
sensor from the fan.

Fit the new sensor ensuring the correct orientation and carefully
tighten the retaining screw.
Refit the fan assembly in reverse order.

23

Fig. 37. Gauze Filter.

Gauze Filter

Positive

Isolating Valve

These instructions should be used when converting appli­ances from natural gas to LPG and vice versa.
Only components supplied by Worcester Heat Systems
should be used.

Only competent persons should attempt the conversion.
Conversion from Natural Gas to LPG should not be
carried out on appliances installed in a room or inter­nal space below ground level.

1.

Ensure the gas service cock is turned OFF and the elec-

trical supply is isolated.

2. Refer to section 14.3 Dismantle the Appliance to
remove the boiler front panel and inner casing. Follow the
dismantling instructions to remove the burner.

3. Remove the injector and replace with the injector from
the kit.

4. Remove the nut, end cap and bracket from the end of
the burner.

4.1 For conversion to Natural gas remove the internal

gauze.

4.2 For conversion to LPG fit the gauze into the burner

body.

5. Refit the end cap ensuring the bracket is in the correct
orientation.

6. Refit the burner to the appliance and re-assemble the
inner casing.

7. Follow the dismantling instructions to remove the gas
valve and refit the new valve. See Installation Instructions:
Section 15.4.11 Replacement of Parts, Component
Replacement, Gas Valve.

8. Turn on the gas and electricity supplies and following
the commissioning procedure confirm gas soundness and
correct boiler operation.

9. Set the gas pressure to the required rate for the new gas
type as specified on the data plate. When this is done refit
the cap to the adjuster and seal its retaining screw with
paint or nail varnish.

10. Turn off the boiler and when cool peel off the arrow
from the data plate and re-stick it against the gas type for
which the appliance is now converted.

11.Replace the boiler front panel.

The conversion is now complete.

16. Conversion Instructions

Item No. Description Natural Gas to LPG Kit LPG to Natural Gas Kit

7 716 192 131 7 716 192 132

1. Burner Injector 8 716 140 209 8 716 140 224
Stereomatic 2.78mm Stereomatic 4.3mm

2. Burner Gauze 8 716 142 601 Remove Gauze

3. Gas Valve 8 716 142 430 8 716 142 413

Parts List

Fig. 38. Flue flow sensor.

24

End of a domestic

hot water overrun

Escape pause by

resetting the mains

electricity supply

OFF-ON

Anti-cycle delay

Main gas valve

OFF

6

EITHER

AUTOMATIC START-UP SEQUENCE

1. Central Heating Mode

NO

PASS

PRESENT

PRESENT

ABSENTABSENTFAIL

YES

Central heating

temperature 5°C

above set point

Operating Switch

(or programmer)

OFF

Fan overrun

4 minutes

Continue

pump overrun

for 6 secs pump

pulse after

2 miniutes.

Gas valve OFF

Room thermostat

OFF

Burner pressure

1.0 mbar for 60

seconds.

Burner pressure

automatically

adjusted for range

rating and then

modulated to

maintain set flow

temperature

AUTOMATIC

START-UP

SEQUENCE

CENTRAL

HEATING

DEMAND

SATISFIED

Water flow

temperature

monitored by central

heating sensor

Pump on

Operating Switch

(or programmer)

and room

thermostat on

CENTRAL HEATING

DEMAND

Internal

"Autofrostat"

demand

Is fan in

overrun mode?

Air pressure

switch test

Fan ON

Sense air

pressure

Main valve

opens

Sense

flame

Initiate

sparking

Stop

sparking

Wait

(fan or fan and

pump on)

Ignition Time -

out (after 9secs)

Ignition

Lock-out

Wait

(fan or fan and

pump on)

Wait (pump on

in central

heating mode)

17. Operational Flow Diagrams

25

Signal from the

flow switch

HOT WATER

DEMAND

(Overrides all other

overrun modes

and functions)

No demand and

primary

temperature below

6°C monitored by

the central heating

sensor

Internal

"Autofrostat"

Demand

Run pump

Below 4°C

Above 8°C

4°C to 8°C

Monitor central

heating sensor

Burner pressure

at 1.0 mbar

6

Burner pressure adjusted

based on the temperature

rise over the previous

minute. Aiming at 4°C

rise/minute.

Burner never to be

extinguished

irrespective of the

rate of temperature

rise

At the set point

change to a wide

band proportional

control

Commence normal central

heating mode until heating

temperature reaches 20°C

Return to normal

OFF state

Pump on until

primary temperature

drops to 50°C

No demand and central

heating temperature above

50°C monitored by the

central heating sensor

End of hot water demand

with no central heating

demand. Hot water

thermistor above 40°C

6 second pump pulse with a

2nd 6 second pump pulse 2

minutes later.

End of demand or central

heating temperature above

70°C monitored by the

central heating sensor

Fan on for

4 minutes

Inhibit operations

for approximately

1 second. 6 second

delay before re-

ignition from any

other demand.

Is the central

heating mode

interrupted?

AUTOMATIC

START-UP

SEQUENCE

HOT WATER

DEMAND

SATISFIED

Pump OFF

Wait for hot water

temperature to

drop to factory

pre-set level

Gas valve OFF.

Fan remains ON

Hot water

temperature above

70°C

Modulate heat

input to maintain

hot water

temperature at the

factory pre-set

level

Gas valve OFF

Fan overrun

4 minutes

Operating

Switch (or

programmer

OFF)

Domestic hot water

temperature

monitored by hot

water sensor

3. "Autofrostat" Function

4. Pump Overrun Function

5. Fan Overrun Function

2. Domestic Hot Water Mode

6. Central Heating ramp control

Pump pulse 6

seconds then 2

minutes later

2nd pulse

26

F1 2ATHRC

F2 1.25AT

Optional links

SparkFlame sense

Outputs Inputs

Mains
indicator

Modulating

valve

Overheat stat

X6 Pins 8 & 9

X6 Pins 15 & 16

X6 Pins 5,6 & 7

X6 Pins 1 & 2

X6 Pins 19 & 20

X6 Pins 3 & 4

Flow signal

CH temp. sensor

DHW temp. sensor

CH control POT

Air pressure switch

MAINS
PROGRAMMER/CLOCK

FULL SEQUENCE

CONTROLLER

GAS VALVE

LOW VOLTAGE
ELECTRONICS

(Microcontroller)

ROOM STAT

X1

X2

321

1

2

3

4

6

5

RL1

X3

Pin 1 X3 Pin 2

X4 Pin 3

X5 Pin 3

X5 Pin 2X5 Pin 1

X4 Pin 1

FAN

PUMP

RL3

RL4

N

N

N

N

L

18. Fault Finding

27

Fault in

Central Heating

Fault in

Domestic Hot Water

Is mains LED flashing?

Is mains LED

iluminated?

Turn control knob

fully clockwise

Set room stat to

call for heat

Ensure link is fitted at

X2 pins 2 & 3

Set clock to call for heat

Has overheat

thermostat tripped

Ensure link is fitted at

X2 pins 5 & 6

Is mains LED flashing?

GO TO

CHECK D

GO TO

CHECK K

GO TO

CHECK K

GO TO

CHECK E

GO TO

CHECK F

GO TO

CHECK O

GO TO

CHECK C

Is control knob

set for demand?

Is a room thermostat

fitted?

Is room thermostat

calling for heating?

Is programmer fitted?

Is programmer calling

for heat?

Is pump running?

Has overheat

thermostat tripped?

Is mains LED

illuminated?

YES

YES

YES

YES

YES

YES

NO

YES

YES

YES

YES

YES

YES

YES

NO

NO

NO

NO

NO

NO

NO

NO

NO

NO

NO

28

No mains LED

Connect mains

supply

Replace fuseIs F1 (2ATHRC) OK?

Is F2 (1.25AT) OK?

Faulty PCB

Replace

Flashing mains LED

Remove

X6

Open circuit

Replace thermistor

Replace harness

Short circuit

Faulty PCB

Replace

Is resistance between

pins 3 & 4 between

690ohms & 33k

Is resistance between

pins 19 & 20 between

690ohms & 33k

Replace fuse

Is mains present at

X1 pins 1 & 3?

GO TO

CHECK H

GO TO

CHECK I

GO TO

CHECK H

GO TO

CHECK J

NO

NO

NO

YES

YES

YES

YES

YES

YES

NO

NO

OK

OK

OK

OK

Faulty

Faulty

Faulty

Faulty

NO

29

The overheat thermostat can be

reset by pressing the reset button,

but if it trips immediately or on a

regular basis a serious problem has

occurred therefore contact your

installer

Reset thermostat

Overheat Thermostat Check

Pump Check

Fan Check

Does button hold in?

Secure Connector

Secure Connector

Faulty pump

Is pump connector

secure on the PCB (X3)?

Is fan connector

secure on the

PCB (X4)?

Is mains present at the

pump connector

(X3 pins 1 & 2)?

Is mains present at the

fan connector

(X4 pins 1 & 2)?

ATTAC H to heat

exchanger

Is capillary broken?

Ensure appliance is

cool and retest

Replace overheat

thermostat

Is capillary firmly

ATTACHED

to exchanger?

GO TO

CHECK I

GO TO

CHECK O

GO TO

CHECK L

YES

YES

YES

YES

YES

YES

NO

NO

NO

NO

YES

NO

NO

NO

Faulty Harness

Faulty fan

YES

Mains at fan

NO

30

Thermistor Check

Harness Continuity Check

Harness Short Check

Remove connectors

from thermistor

Thermistor OK

Remove appropriate

connectors

Is continuity observed

between each end of

wire in question?

Faulty harness

or connector

Harness OK

Remove appropriate

connectors

Faulty harness

Harness OK

Is short circuit

observed between pair

of wires in question?

Is resistance between

terminals of thermistor

between 690ohms & 33k

Faulty thermistor

YES

YES

YES

YES

NO

NO

YES

YES

NO

31

Ignition Check

Is fan running?

Is sparking present at

the electrodes?

Faulty PCB

Replace

Connect ignition leads

securely

Are leads breaking

down?

Ignition coil faulty

replace PCB

Replace leads

Does burner continue?

Does gas pressure

modulate?

Ignition OK

Faulty PCB

Replace

Is flame sense

electrode in flame?

Is lead secure

both ends?

Secure lead

Ensure flame sense

electrode in flame at

minimum burner

pressure

Are ignition leads

connected both

ends securely?

Does sparking occur?

Does ignition occur?

YES

YES

YES

YES

YES

HARNESS OK

YES

YES

YES

YES

YES

NO

NO

NO

NO

NO

NO

NO

NO

NO

NO

GO TO

CHECK G

GO TO

CHECK E

GO TO

CHECK M

GO TO

CHECK I

GO TO

CHECK N

GO TO

CHECK L

32

Remove BROWN and

WHITE terminals

from air pressure

switch

Air pressure switch

faulty

With no demand, is a

short-circuit observed

at exposed APS

terminals?

Reconnect the

WHITE & BROWN

wire and remove the

GREEN wire. Initiate

a demand.

Does the fan run?

PCB faulty

Air pressure switch

faulty

APS OK

Is gas pressure present

at input to gas valve?

Ensure gas supply

Faulty board

Replace

Faulty gas valve

Replace

Is live output present at

X5 pins 1 & 2 relative to

neutral at pin 3?

Is gas pressure present

at input to burner?

Gas valve OK

With fan running

disconnect BROWN

wire. (DO NOT touch

chassis with it). Is a

short circuit observed

across exposed APS

terminals?

Gas Valve Check

NO

NO

NO

YES

YES

YES

YES

YES

NO

NO

NO

Air Pressure Switch Check

Is there mains 230V
at fan connector X4

pins 1 and 3?

YES

Fan or fan cable

faulty

NO

YES

L

With pressure above

minimum, remove Modureg

Lead. Does pressure drop to

minimum?

33

Is minimum pressure

observed at burner at all

times?

Modulating Valve Check

Flow Switch Check

GO TO

CHECK I

YES

YES

GO TO

CHECK I

YES

YES

NO

NO

HARNESS OK

YES

YES

NO

NO

NO

NO

Is pressure at burner

always the same?

Is resistance

nominally 125ohms

Does voltage

go above 6.25V

Faulty PCB.

Replace

Reconnect X6 and measure

voltage across modulating

valve during operation

Gas valve OK

Remove

X6

Close all taps to set no

domestic flow

Faulty flow switch.

Replace

Faulty flow switch.

Replace

Is short circuit observed

at

X6 pins 1 & 2

Is open circuit observed

at X6 pins 1 & 2?

Open a tap fully to set

domestic flow

Flow Switch OK

Faulty modulating valve .

Replace gas valve

Remove X6, measure

resistance between

pins 15 & 16

N

YES

NO

34

Key G.C. No. Part Manufacturer’s Reference Qty WHS
No. Part No.

1 E01-579 Burner Assembly Natural Gas Aeromatic AC23/053586 1 8 716 142 604 0

E01-580 Burner Assembly LPG Aeromatic AC23/053587 1 8 716 142 611 0

2 E01-591 Injector Natural Gas Stereomatic O 4.3mm 1 8 716 140 224 0

E00-741 Injector LPG Stereomatic O 2.78mm 1 8 716 140 209 0

3 E01-892 Gas Valve Natural Gas SIT 1 8 716 142 413 0

E01-893 Gas Valve LPG SIT 1 8 716 142 430 0
4 E01-596 Air Pressure Switch Huba 605.99484 1 8 716 142 414 0
5 375 697 Spark Electrode Assembly Buccleuch 1 8 716 142 100 0
6 E01-612 Flame Sensor Buccleuch 1 8 716 120 345 0

E01-930 Flame Sensor Harness 1 8 716 120 126 0
7 E01-598 Ignition Harness Buccleuch 1 8 716 120 236 0
8 E01-599 Gas to Water Heat Exchanger Giannonni 1 8 716 142 905 0
9 E01-600 Insulation Pack WHS 1 7 716 192 216 0

10 E01-601 Auto Air Vent Intermes 1 8 716 140 504 0

11 299-506 Pressure Gauge Cewal 1 8 716 142 300 0
12 375 699 Pressure Relief Valve Caleffi 3141 3bar 1 8 716 142 404 0
13 E01-602 Pump with Harness Grundfos 15 60 special 1 8 716 143 107 0
14 E01-603 Expansion Vessel (8Ltr) 389mm Dia Winkelman Panhof 1 8 716 142 502 0
15 E01-604 PCB Boiler Control Pactrol 1 8 716 146 300 0
16 E04-582 Temperature Thermistors Elmwood 2 8 716 142 384 0

E01-900 CH Thermistor Clip 1 8 716 148 313 0

299-495 DHW Thermistor Clip 1 8 716 148 303 0
18 E01-605 DHW Flow Regulator 1 8 716 141 052 0
19 324-822 Gauze Filter WHS 1 8 716 148 401 0
20 299-363 Flow Sensor WHS 1 8 716 141 000 0

21 E01-606 Fan Assembly SIFAN 1 8 716 120 993 0
22 E01-607 Safety Temperature Limiter Ranco LM7 1 8 716 142 307 0
23 E01-886 Flow Switch Assembly SIKA 1 8 716 120 971 0
24 299-357 Fuse Pack WHS 1 7 716 192 206 0
25 E01-610 Gasket Pack WHS 1 7 716 192 218 0

ACCESSORIES

299-360 Mechanical Programmer Kit Deihl 7 716 192 002 0

E01-940 Gas Conversion Kit NG to LPG 7 716 192 131 0
E01-941 Gas Conversion Kit LPG to NG 7 716 192 132 0
E05-341 Mini Expansion Vessel Kit Including new pipe and Expansion Vessel 7 716 192 188 0

FLUE OPTIONS

E01-942 Telescopic Horizontal Flue Kit 127-350 mm 7 716 191 005 0
E01-943 Extension Flue Kit 750 mm 7 716 191 006 0
E01-944 Vertical Flue Kit 7 716 191 015 0
E01-945 Vertical Flue Adaptor 7 716 191 016 0
E01-946 Internal Fixing Kit Telescopic Flue 7 716 191 019 0
E01-058 Flue Elbow Kit 90 deg. 7 716 191 013 0
E01-059 Flue Elbow Kit 45 deg. 7 716 191 014 0

19. Component Parts List

35

9

8

14

3

21

1

15

13

4

22

11

7

12

10

23

20

6

25 24

2

19

18

16

23

This booklet is accurate at the date of printing but will be superseded and should be disregarded if specifications and/or appearances are changed in the interests

of continued improvement.

All goods sold are subject to our official Conditions of Sale, a copy of which may be obtained on application.

PUBLICATION 8 716 145 028C 11/98

Bosch Group

Worcester Heat Systems Limited, Cotswold Way, Warndon, Worcester WR4 9SW.

Telephone: [phone]. Fax: [phone].

Technical Helpline [phone].