Worcester 28I RSF User guide

28i RSF

WALL MOUNTED COMBINATION BOILER FOR CENTRAL HEATING

AND MAINS FED DOMESTIC HOT WATER

INSTALLATION AND

SERVICING INSTRUCTIONS

This appliance is for use

with Natural Gas

Cat I

2H

GC NUMBER

N.G. 47 311 54

BOILER OUTPUT

To Domestic Hot Water – To Central Heating –

Modulated Control Modulated Control

Minimum 8.5 kW Minimum 10.5 kW
Maximum 27.5 kW Maximum 27.5 kW

THESE INSTRUCTIONS APPLY IN THE UK ONLY AND MUST BE LEFT WITH THE

USER OR AT THE GAS METER.

READ THE INSTRUCTIONS BEFORE STARTING WORK - THEY HAVE BEEN

WRITTEN TO MAKE THE INSTALLATION EASIER AND PREVENT HOLD-UPS.

This appliance must be installed by a competent person in accordance

with the Gas Safety (Installation and Use) Regulations 1998

1.1 Gas Safety (Installation and Use) Regulations, October 1998

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 1998 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.
BS5440:1:2000 Flues and Ventilation for gas appliances of rated
input not exceeding 60 kW: Flues.
BS5440:2:2000 Flues and Ventilation for gas appliances of rated
input not exceeding 70kW: Air Supply.
BS6891:1988 Installation of low pressure gas pipework
installations up to 28mm (R1).
BS7593:1993 Central Heating system cleansing and flushing.

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.

1.8 Product Liability regulations indicate that, in certain
circumstances, the installer can be held responsible, not only for
mistakes on his part but also for damage resulting from the use of
faulty materials. We advise that, to avoid any risk, only quality
approved branded fittings be used.

The Benchmark initiative is the new code of practice to

encourage the correct installation, commissioning and servicing
of domestic central heating boilers and system equipment.

The 'Log-book' is a vital document that must be completed
by the installer at the time of installation. It confirms that the
boiler has been installed and commissioned according to the
manufacturers instructions.

Without the completion of the Log-book, manufacturers may
refuse to respond to a call-out from a householder, who will be
advised that he or she must call back the installer, who has not
fulfilled his obligations to record the information required by the
initiative.

It is important that:

The services and the system are properly flushed as specified.
The User is clearly instructed on the correct operation of the
appliance.
The benefits of regular servicing are explained - to maintain the
efficiency and extend the life of the appliance.

2.1 General Information
The appliance is set to give the maximum output of 27.5 kW to
the domestic hot water and to the heating system. The hot water
flow rate is limited to a nominal 10 l/min at a maximum
temperature rise of 40°C.
The sanitary water section of the appliance is suitable for mains
water pressure of up to 10bar.

2.2 Electrical Supply
230V - 50Hz. Load 180 watts. External fuse 3A, Internal fuses F1

- 2A, F2 - 1.0A (20mm).

2.3 Gas supply
The appliance requires a maximum of 3.17 m

3

/h of natural gas
(G20). The installation and the connection of the gas supply to
the appliance must be in accordance with BS6891.
The meter or regulator should deliver a dynamic pressure of 20
mbar (G20) at the appliance, which is equivalent to about 19-

19.5 mbar at the gas valve inlet pressure test point.

2.4 Installation
The appliance is suitable for indoor installation only and for use
with a sealed system only.
Do not place anything on top of the appliance.
It is a room sealed appliance and a separate combustion air
supply is not required in any room or compartment in which the
appliance is fitted.
If the appliance is fitted in a cupboard or a compartment is built
around it after installation, then the structure must conform to
the requirements of BS6798 and BS5440 Part 2. However,
because of the low casing losses, there is not a need for the
cooling ventilation openings in the compartment. The spaces

specified in Section 6.3 must be maintained.

There is space for the service pipes to pass at the back of the
appliance.

2.5 Flue

The appliance has a multi-directional fanned flue system.
The standard telescopic flue assembly length is from 330mm to
725mm.
Extension flue kits are available for flue lengths up to 2500mm.

2. Introduction1. Installation Regulations

2

1. Installation Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2 11. Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 10

2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2 12. Installing the Appliance. . . . . . . . . . . . . . . . . . . . . . . . . . Page 13

3. Technical Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 4 13. Commissioning the Appliance . . . . . . . . . . . . . . . . . . . . Page 18

4. Siting the Appliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 6 14. Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 20

5. Siting the Flue. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 7 15. Inspection and Service. . . . . . . . . . . . . . . . . . . . . . . . . . . Page 21

6. Air Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 7 16. Replacement of Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 22

7. Sealed System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 8 17. Operational Flow Diagrams. . . . . . . . . . . . . . . . . . . . . . . Page 27

8. Open Vent System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 8 18. Fault Finding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 29

9. Domestic Hot Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 9 19. Component Parts List. . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 37

10. Gas Suppy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 9

Contents

An optional vertical flue kit to provide for flue lengths up to
3400mm 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.

2.6 Controls
Central Heating Temperature control knob.
A facia mounted programmer is provided.
A room thermostat and/or an externally mounted programmer
for mains voltage operation may be connected to the appliance.

2.7 System

All dirt must be flushed from the system before
operating the appliance.
The connections in the system must withstand a pressure of
upto 3 bar.
Radiator valves must conform to BS2767: 10:1977.
Table 3 gives the pump head available for the system and the
required temperature differential.
A drain cock must be fitted to the lowest point and an air vent to
the highest point of the system.

2.8 Showers, Bidets, Taps and Mixing Valves
All taps and mixing valves must be suitable for the available
mains pressure and temperatures up to 55°C. It may be
necessary to fit a pressure reducing valve.
Hot and cold mains fed water can be supplied to over-rim bidets
but is subject to local water company requirements.
The flow of water from individual outlets varies on all mains fed
systems that are not fitted with flow balancing valves. If a
pressure equalising valve is fitted then the domestic hot water
temperature should be set to maximum.
Thermostatically controlled shower valves give extra comfort
and protection.

2.9 Safety
The appliance must not be operated with the inner casing cover removed.
The gas and electricity supplies must be turned off before
working on the appliance.
Temperature monitoring controls are fitted to prevent overheating.
Automatic frost protection is provided together with automatic
pump seizure protection.
The gas valve solenoids are automatically checked for gas soundness.

IMPORTANT: Where back-flow prevention devices, including
water meters, are fitted the expansion of hot water into cold
water main can be prevented. This can result in a pressure
build-up that may cause damage to the boiler and household
devices such as showers, washing machines etc.

In these cases we recommend that a mini-expansion vessel
be fitted adjacent to the boiler in the cold water pipe.

2.10 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 will 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 10.5 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 will 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 will continue
to run to dissipate the residual heat from the appliance as necessary.

3

Fig. 1. Facia controls

1

2

3

1 Mains Indicator Light
2 System Pressure Gauge
3 Central Heating Temperature Control

Fig. 2. Water flow diagram.

1 2 4 5

3

6

7

8

9

10

11

12

1 Safety Discharge 10 Bi-thermal Gas to Water
2 C.H. Flow Heat Exchanger
3 Domestic Hot Water Out 11 Domestic Water Flow
4 Domestic Cold Supply Turbine
5 C.H. Return 12 Pressure Relief Valve
6 Fixed By-pass
7 Circulating Pump
8 Sealed System Expansion

Vessel

9 Automatic Air Vent

The data plate is fixed to the inner casing cover.

3. Technical Data

4

NOMINAL BOILER RATINGS (10 Minutes After Lighting)

BOILER ADJUSTED FOR G20 (Natural Gas)

OUTPUT INPUT (Net) GAS RATE

kW kW m bar. m

3

/h

8.5 10.5 1.0 1.11

10.5 13.5 1.5 1.38

27.5 30.0 13.5 3.17

Table 1.

BURNER

PRESSURE

MAXIMUM AVAILABLE PUMP HEAD

BOILER OUTPUT HEAD MIN. FLOW RATE

kW Metres L/min. °C

10.5 4.19 13.7 11

27.5 2.0 27.5 14

Table 3

MECHANICAL SPECIFICATIONS

CENTRAL HEATING FLOW - COMPRESSION 22mm

RETURN - COMPRESSION 22mm

COLD WATER INLET - COMPRESSION 15mm

DOMESTIC WATER FLOW - COMPRESSION 15mm

GAS INLET Rp

1

⁄

2

RELIEF VALVE DISCHARGE (PUSH FIT) 15mm

CASING HEIGHT 800mm

CASING WIDTH 450mm

CASING DEPTH 360mm

WEIGHT - LIFT 42.3kg

WEIGHT - UNPACKED (DRY) 45.8kg

WEIGHT - PACKAGED 52kg

Table 4

FLUE DETAILS

HORIZONTAL FLUE mm

WALL HOLE DIAMETER EXTERNAL FIX 110

INTERNAL FIX 150

STANDARD FLUE MINIMUM LENGTH 330/425 *

MAXIMUM LENGTH 725

EXTENDED FLUE MAXIMUM LENGTH 2500

FLUE ASSEMBLY DIAMETER 100

Table 2.

FLOW/RETURN

DIFFERENTIAL

Natural Gas: Net Input = Gross Input x 0.901
* Hot water setting - manual adjustment
**Central heating setting - non adjustable

* NOTE : Flue lengths between 330 and 425mm require the flue to be cut

*
**

5

GAS SUPPLY SYSTEM

Table 7

CLEARANCES (mm)

INSTALLATION SERVICE

ABOVE APPLIANCE AND/OR FLUE ELBOW 30 30
IN FRONT OF APPLIANCE 600 600
BENEATH APPLIANCE 200 200
RIGHT AND LEFT HAND SIDE 10 10

Table 8

SYSTEM CAPACITY

TOTAL SYSTEM VOLUME litres

INITIAL INITIAL CHARGE PRESSURE bar
PRESSURE bar 0.5 1.0 1.5

1.0 57 75 N/A

1.5 31 42 52

Table 9

PERFORMANCE SPECIFICATIONS

PRIMARY WATER CAPACITY litres 3.0

MAXIMUM MAINS INLET PRESSURE bar 10

MINIMUM MAINS INLET PRESSURE (WORKING) FOR MAXIMUM FLOW bar 0.9

MINIMUM MAINS INLET PRESSURE (WORKING) FOR OPERATION bar 0.1

MAXIMUM CENTRAL HEATING FLOW TEMPERATURE °C 82 (nom)

MAXIMUM CENTRAL HEATING SYSTEM PRESSURE (OPERATING) bar 2.5

MINIMUM CENTRAL HEATING SYSTEM PRESSURE bar 0.5

OUTPUT TO DOMESTIC HOT WATER kw NATURAL GAS (G20) 8.5 - 27.5

OUTPUT TO CENTRAL HEATING kw NATURAL GAS (G20) 10.5 - 27.5

DOMESTIC HOT WATER SPECIFIC RATE - D 30°C RISE l/min 13.1

MAXIMUM DOMESTIC HOT WATER FLOW RATE - 40°C RISE l/min 9.8

NOx CLASSIFICATION Class 2

SEDBUK NUMBER 78.1

SEDBUK BAND D

BURNER INJECTOR mm 4.5

Table 5

Refer to Section 6.

DOMESTIC HOT WATER TEMPERATURE RISE

DISCHARGE RATE l/min 7 8 9 10
TEMPERATURE RISE °C 56 49 44 39

Table 6

Total length of gas supply pipe Pipe size

(metres) (Ømm)

36912

Natural Gas

8.7 5.8 4.6 – 22

18.0 12.0 9.4 – 28

Gas

Discharge

Rate

(m

3

/hr)

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 total length.
i.e: Bend=0.5 metre, Tee=0.5 metre, 90° Bend=0.3 metre.

4.1 The appliance may be installed in any room but refer 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 NO special wall protection is required.

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

appliance. See Table 4.

4.5 The specified clearances must be available for installation
and for servicing. See Fig. 3 and 4. (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 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. Siting The Appliance

6

Fig.4. Appliance casing dimensions and

required clearances (side view).

All dimensions in mm

Fig. 5. Side flue opening

Fig. 3. Appliance casing dimensions and

required clearances (front view).

All dimensions in mm

30

170

10

10

All dimensions in mm

450

106

600

200

800

222

360

200

222

200

Fig. 6. Appliance pipework connections.

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

(A)

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. Refer to Fig. 7.

5.3 If a terminal is fitted less than 2 metres above a surface to
which people have access then a guard must be fitted. The guard
must be evenly spaced around the terminal and fixed with
plated screws. A type K2 guard is available from Tower Flue
Components, Vale Rise, Tonbridge, TN19 1TB.

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

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

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

5.7 The standard flue kit is horizontal and extends from 425 to
725mm in length. It can be shortened to 330mm (for single brick
wall applications) by cutting the flue ducts if required. Extension
kits are available for flue lengths up to 2500mm. A vertical flue
system for heights upto 2.3m plus the terminal assembly. Refer to
Table 2.
45° and 90° bends are available.

6.1 A separate vent for combustion air is not required.

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

7

L

L

K

K

F

F

G

A

M

EJF

HI

D

G

A

B,C

Fig. 7. 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

other opening e.g. air brick. 300mm J– From an opening in a car port (e.g. door
B– Below gutters, soil pipes or drain pipes. 75mm window) into dwelling. 1200mm
C– Below eaves. 25mm K– Vertically from a terminal on the same
D– Below balconies or car port roof. 25mm wall. 1500mm
E– From vertical drain pipes and soil pipes. 25mm L– Horizontally from a terminal on the same
F– From internal or external corners. 25mm wall. 300mm
G– Above ground, roof or balcony level. 300mm M–From door, window or air vent
H– From a surface facing a terminal. 600mm 300mm

Above the Turret 30mm

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 300cm

2

150cm

2

LOW LEVEL 300cm

2

150cm

2

7.1 The system must comply with the requirements of BS 6798
and BS 5449 and the appliance must not be operated without
the system being full of water, properly vented and pressurised.

7.2 The pressure relief valve operates at 3 bar (45lb/in

2

). The
discharge must be directed away from electrical components or
where it might be a hazard to the user.

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

7.4 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).

7.5 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.

7.6 The filling point must be at low level. Refer to Fig. 8.

7.7 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. A filling loop kit is supplied.

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

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

7.10 The pump is set at maximum and should not be adjusted.

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

3 bar.

7.12 Radiator valves must conform to BS 2767:10.

7.13 Other valves used should conform to the requirements of

BS 1010.

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

The appliance is NOT suitable for connection to an open vented
system.

8. Open Vent System

8

Fig. 8. Sealed primary water system.

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.

Refer to

Fig. 2.

7. Sealed System

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.
Refer to Section 19.
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

) and is fitted with a mains supply isolating valve.

9.5 The maximum domestic hot water flow rate is 11.4
litres/min (±15%).

9.6 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.

9.7 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.

9.8 Hot and cold taps and mixing valves used with this
appliance must be suitable for operating at mains pressure and
temperatures of 55°C.
Note: The maximum domestic hot water outlet temperature is
fixed at 55°C and it is not adjustable.

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

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

9.11 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.

9.12 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.

9.13 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.

9.14 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 metres 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.

The boiler requires 3.17m

3

/h (112ft3/hr) of natural gas with a

calorific valueof 37.78MJ/m

3

. The meter govenor should deliver
a dynamic pressure of 20 mbar (8in w.g.) at the appliance,
equivalent to a pressure of 19-19.5 mbar at the gas valve on
natural gas.
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 BS6891.

9. Domestic Hot Water

9

10. Gas Supply

11.1 MAINS SUPPLY.

230 V ~, 50 Hz, 180 watts.
External Fuse: 3A. Internal Fuses: 2A SLOW (F1), and 1A
FAST(F2).
Spare fuses are supplied with the appliance and are fixed
adjacent to the pressure gauge.

11.2 It must be possible to completely isolate the appliance.

11.3 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.

11.4 The appliance must be earthed.

11.5 Mains Cable. 0.75mm

2

(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. 11. The earth lead must be slack when the others are taut.

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

11.7 If a room thermostat and/or external programmer is to be
fitted refer to Figs 12 and 13. The devices must be suitable for
use with mains voltage.

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

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

11.10 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 at the programmer).
Connection must be made at X2 terminals RI and CL. refer to Fig.

28. For advice on external frost thermostats contact Worcester
Heat Systems Technical Helpline

11.11 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.

11. Electrical

10

Fig. 9. Wiring diagram.

Overheat

thermostat

DHW sensor

CH

sensor

Gas

valve

Pump

Main

Reg

Flow turbine

Air

pressure

switch

Spark transformer

Mains in

2 Blue

2 Red

2 Yellow

2 Orange

Blue

Blue

Brown

Link

Link

X1

X2

X3

X6

X5

X4

Flame sense
electrode

Spark
electrode

Brown

White

Green

COM

NC

NO

Yellow

Blue

Fan

Brown

Brown

Brown

Black

Green

White

1

2

3

11

Fig. 10. Functional flow diagram.

F1 2A

F2 1AT

Optional links

Spark

Flame sense

Outputs Inputs

Mains
indicator

Modulating

valve

Overheat stat

X6 Pins 8 & 9

X6 Pins 15 & 16

X6 Pins 5,6 & 7

X6 Pins 14,17 & 18

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

GA S VALVE

LOW VOLTAGE

ELECTRONICS

(Microcontroller)

ROOM STAT

X1

X2

3

2

1

1

2

3

4

6

5

RL1

X3 Pin 1

X3 Pin 2

X4 Pin 3

X5 Pin 3

X5 Pin 1

X4 Pin 1

FAN

PUMP

RL3

RL4

N

N

N

N

L

12

Fig. 11. Mains electricity connections.

Brown

Strain relief clamp

Blue

Brown

Green/yellow

Green/yellow

Programmer and room

thermostat

230V

X1

X2

NL

Blue

Fig. 12. 230V room thermostat connections.

Fig. 13. 230V programmer connections.

RN RI

X2

Remove link

Neutral

Switched live

Live

RL

CN

Motor

CI

X2

Neutral

Switched live

Live

CL

Remove link

Technical Helpline.

Note: READ THIS SECTION FULLY BEFORE COMMENCING
INSTALLATION.

12.1 General

The appliance is only suitable for fitting to a sealed system.
The flue must be installed as specified in BS5440:1.
Check that the appliance is suitable for the local conditions. i.e. gas
supply.

12.2 Unpacking

Remove the appliance from its packaging and check the contents
against the packing list.

12.3 Site Preparation

Check the correct position for the appliance has been chosen.
Refer to Section 4 and Table 8.
Check that the wall is flat and and will support the weight of the
appliance. Refer to Table 4.

12.4 Fixing Holes ad Flue Opening

Hold the template against the wall.
Check that the template is level.
Mark the position of the fixing holes and the flue opening. Refer to Fig. 14 and 15.

Mark the centre-lines of the pipe connections to aid the pre­plumbing of the system pipework.
Check the position of the fixing points and the flue opening before
drilling the fixing holes 60mm deep for the No.12 size plugs and
cutting the flue duct hole at 110mm diameter (150mm diameter for
internally fitted flues.

12.5 Wall Mounting Plate and Manifold

Fit the plugs and fix the top support to the wall. Refer to Fig. 14.
Check the top support is properly aligned before tightening the screws.

12.6 Gas and Water Pipes

Remove the gas cock and fix the appropriate fitting to connect the
inlet pipe and re-fit.
Pre-plumbing is not recommended if no movement in the pipes is available.
If it is necessary for the pipes to run up the back of the appliance
then they must be arranged to pass behind the expansion vessel.
Pipework must not run horizontally within the limits of the casing.
It is important that the pipes are not fixed near the appliance using
clips that put a strain on the connections.

Before the appliance is fitted to the wall thoroughly

flush the system and mains water supply.

12.7 Install the Boiler

Remove the cabinet by releasing the sides and lifting from the top
location.
Check that the gas and water valves are closed.
Lift the appliance to the wall, engage in the top support. Fix and
tighten the bottom screws. Refer to Fig. 14.
Tighten the gas and water connections.
Fit a discharge pipe to the relief valve leading it away from any
electrics or where it might be a hazard.
The pipe must not be less than 15mm in diameter and must run
continuously downward outside the appliance. Refer to Fig. 6.

12. Installing The Appliance

13

Fig. 14. Appliance mounting plate and flue position.

Fig. 15. 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

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

Mounting wall

Side wall

222mm

166mm

12.8 Air and Flue Duct Preparation

The method of installation of the flue system may be varied to
suit the actual site conditions. The instructions for connecting
and fixing the ducts must, however, be strictly followed.

Remove all packing material from the flue components.

Horizontal Flues up to 725mm Length

Fit the flue restrictor ring by unscrewing the flue spigot from the
boiler. Refer to Fig. 17.

The standard telescopic flue assembly is suitable for flues from
425mm (without cutting) up to 725mm measured from the
centre-line of the boiler flue outlet to the outer face of the wall.
Refer to Fig. 18.

If L is greater than 725mm then flue extension kits will be
required - each kit extends the flue by 750mm up to a maximum
of 2-5m. See table below.

EXTENSION MAXIMUM FLUE LENGTH mm

1 1475
2 2225
3 2500

12.9 Measure and Cut the Ducts
General: Cut the ducts as necessary, ensuring that the ducts are

square and free from burrs. Always check the dimensions before
cutting.
Measure the distance L. Refer to Fig. 20 and 21 .

The standard flue can be telescopically adjusted to any length
between 425mm and 725mm.
Fix the flue assembly together using the self-tapping screw
provided. Refer to Fig. 18.

It will only be necessary to cut the standard assembly if L is less

than 425mm. Cut the flue turret assembly and

the terminal
assembly by the same amount i.e L=350 - remove 75mm from
each

assembly.

Minimum side flue length = 335mm (accommodating a
10mm Service clearance and a 100mm wall)

Minimum rear flue length = 322mm (accommodating a
100mm wall)

If L is between 1175 - 1475mm (1 extension)

1925 - 2225mm (2 extension)

it is not necessary to cut the ducts.

14

Fig.16. Appliance casing and control

equipment fixings.

Inner casing
cover screws
(4)

Side casing
fixing screws
(4)

Facia panel
fixing screws
(2)

Connections
cover fixing
screws (3)

Fig.17. Flue turret fixing and automatic

air vent.

1

2

3

4

5

6

1. Flue spigot fixing screws

2. Flue spigot

3. Restrictor ring

4. Flue spigot fixing holes

5. Reset button

6. Flue gas test point

Restrictor Ring Size

75mm horizontal flue up to 725mm.

Fig.18 . Standard flue assembly.

Appliance casing

Fixing screw

Turret
assembly

Terminal
assembly

L

Telescopic

adjustment

If L is between:

725 - 1175mm (1 extension)
1475 - 1925mm (2 extension)
2225 - 2500mm (3 extension)

it is necessary to shorten the assembly by cutting the first
extension duct assembly i.e. L = 1000mm - remove 175mm
from the air and flue ducts.
NOTE: Extension duct measurements do not include the
socketed end. Unless specifically instructed the socketed end
must not be removed.

Fix the flue ducts together before fixing the surrounding air duct,
the cut ducts fit into the flue assembly.

12.10 Fitting the Flue Assembly with Access to the Terminal

Prepare the flue duct assembly as described in Section 12.9.
Apply the plastic tape to the air duct in contact with the external
brickwork.
From inside push the assembly through the wall. Align the flue
turret and push fully onto the spigot on the appliance. Tighten
the clamping ring and fix with the screw provided. Refer to Fig.

22.

Make good the internal wall face and the external brickwork or
rendering.

Replace the inner casing.

12.11 Fitting of the Flue Assembly without access to the Terminal

A rubber gasket kit is available from Worcester Heat Systems.
NOTE: A larger diameter opening in the wall is required. Refer to
Table 2.

Prepare the flue assembly as described in Section 12.9.

Fit the rubber sealing gasket centrally onto the terminal
assembly and tighten the clamp. Refer to Fig. 23.
Apply the plastic tape to the air duct in contact with the external
brickwork.

From inside push the assembly through the wall so that the
gasket flange is against the outer face. Refer to Fig. 23.
It may be necessary to adjust the legs of the flue centering ring.
Align the flue turret and push fully onto the socket on the
appliance. Tighten the clamping ring and fix with the screw
provided. Refer to Fig 22.
Seal the gap around the duct at the inner wall face with the
flexible seal provided and make good.
Replace the inner casing.

15

Fig. 19. Extension Duct.

L

Appliance casing

Fixing screws

Fixing screw

Turret
assembly

Terminal
assembly

Ducts of equal length

Shorten first extension fitted

to the turret assembly if more

than one extension is fitted

Fig. 20. Flue duct length (side flue).

L

Flue
Turret
assembly

Terminal
assembly

Fig. 21 . Rear flue.

Rear face of appliance
and face of mounting
wall

External
wall face

L

Indents
in line
with wall
face

Terminal
assembly

12.12 Flue Bends

90° and 45° bends are available. A maximum of two bends may
be used in addition to the first bend on the flue turret.
A 90° bend is equivalent to 750mm of straight duct.
A 45° bend is equivalent to 375mm of straight duct.

A maximum flue assembly of 2.5m is possible with 1 X 90° bend
and 2m with 2 X 90° bends.
Measure the lengths X,Y and Z. Refer to Fig. 24.
The maximum value of X using the turret assembly only in
506mm. Reduce the ducts to the appropriate length i.e. X =
406mm, cut 100mm from the air duct and 120mm (to cover the
entry into the 45° or 90° elbow) from the flue duct. Refer to
Fig.24.
NOTE: The flue system ducts between the elbows, dimension Y,
requires the socketed ends (of the first extension if two or more
are used) to be removed and the air and flue tubes to be cut to
the same length.
Cut the ducts to a length Y - 162mm. Refer to Fig. 24.
The final section, dimension Z, of the flue system must include a
section of plain duct assembly i.e . an extension assembly with
the sockets removed. Reduce the final section, including the
terminal assembly, by the appropriate amount i.e. Air duct Z ­81mm and the flue duct Z - 51mm. Refer to Fig. 24.

If Z<425mm it will be necessary to cut the air and flue ducts of
the extension to a plain length of 100mm and reduce the length

of the terminal assembly i.e Z=350mm - remove 75mm from the
terminal assembly.
If Z in 425 - 725mm it is not necessary to cut the terminal
assembly or use a second extension duct as the length can be
set telescopically.
If Z>725mm then two extension duct assemblies will be
required, the first assembly being cut to length as plain tubes.

If more than two extension ducts are needed in any section to
achieve the required length then the final section of the
assembly must not be less than 325mm without cutting the
terminal assembly.
NOTE: The flue duct of the final extension must be 30mm longer
than the air duct.

Each section must be connected to the previous section of the
flue bend by fixing the flue ducts together and then similarly
fixing the air ducts which engage the elbows.

Fit the assembly as described in Section 12.10, 12.11 as
appropriate.
Make good the internal and external brickwork or rendering.

16

Fig. 22. Flue Turret Fixing .

Fig. 23. Terminal assembly for internal

fitting of the flue.

5

4

1

3

2

1. Flue centering ring

2. Air duct

3. Flue duct

4. Rubber sealing gasket

5. Flue Terminal

Fig. 24. Flue bends.

Air Z – 81mm

Flue Z – 51mm

Z

Y

X

Y – 162mm

(plain tube)

1

4

2

3

1. Flue turret

2. Clamp

3. Appliance

4. Fixing Screw

Rubber sealing
gasket

Clamping ring

Flue terminal

12.13 Vertical Adapter for Horizontal Flues

An adapter is available for an initial short section of vertical flue.
Refer to Fig. 26.
Measure and cut the flue as described in Section 12.12.
The first, vertical, section (equivalent to dimension X) is
measured from the top of the boiler casing. Cut the vertical
section of the extension duct to 167mm less than the measured
distance. Do not remove the socketed ends.
The minimum measured distance is 167mm.
Seal the air duct to the turret using silicone sealant.
Fix the adapter with the clamp and screw provided.

12.14 Completion of the Installation

Check that all the connections on the appliance have been
tightened.
Remove the facia bottom panel. Refer to Fig. 27.

Connect the mains electricity supply lead to the appliance and
secure the cable clamp. Refer to Fig. 27. and 28.
Check there is sufficient loose lead to allow the release of the
facia panel assembly and that the earth lead of the mains supply
cable is longer than the live and neutral leads.

Fit the facia mounted clock. Full instructions are sent with the
programmer. Refer to Fig. 28. and 29.

Connect any external controls ensuring that the leads pass
through the appropriate clamps. Refer to Fig.18.

Test for gas soundness as described in BS6891.

If the appliance is not to be commissioned immediately, replace
the cabinet and facia bottom panel. Check that the gas and
electricity services have been turned off.

17

120mm

100mm

Fig. 25 - Elbow to Flue Turret

Assembly.

Fig. 26 Vertical Adapter.

Flue Duct

Air Duct

Adapter

Clamp

Flue Spigot

Flue Turret

Bend

Fig. 27 - Facia Connections Cover.

1

2

3

4

5

1. Control Panel Fixing Screws

2. Facia

3. Control Panel Pivot Point

4. Connection Cover

5. Connection Cover Fixing
Screws

Fig. 28 -

N. L.

Mains

Fuse 2A Slow Blow

Earth

C

N CI CL

Programmes

RN RI RL

Room Thermostat

Gas Valve

Fan

Pump

Benchmark Water Treatment: For optimum performance after
installation, this boiler and its associated central heating
system should be flushed in accordance with the guidelines
given in BS7593:1992 - Treatment of water in domestic hot
water systems. Full instructions are supplied with proprietary
cleansers sold for this purpose. If an inhibitor is to be used
after flushing, it should be used in accordance with the
inhibitor manufacturers instructions.
Suitable flushing agents and inhibitors are available from Betz
Dearborn Tel: [phone] and Fernox Tel: [phone].
Instructions for use are supplied with these products.

13.1 Remove the appliance cabinet

Check that the electrical supply and the gas supply to the
appliance are turned off and that all the water connections
throughout the system are tight.
Open the system valves at the appliance. Refer to Fig.6 .
Remove the automatic air vent cap. Refer to Fig. 30 .
Fill the system through the external filling loop. Refer to Section
7, Sealed System.
Vent each radiator in turn.
The automatic air vent will vent the appliance.
Remove the cap from the pump and turn the shaft about a half
turn.
Replace the cap. Refer to Fig. 31.
Switch on the electricity supply (not the gas) and set the controls
to give continuous operation in the CH mode.
When the air is expelled turn off the electrical supply and the CH
control to off.
Check the pressure relief valve operates by turning the knob anti­clockwise until it releases.
Lower the facia to gain acces to the relief valve. Refer to Fig. 32.
Water should be expelled from the discharge pipe.

13.2 Set the Expansion Vessel Pressure

The charge pressure of the expansion vessel as despatched is

0.5bar, which is equivalent to a static head of 5m (17ft).
The charge pressure must not be less than the static head at the
point of connection.
A Schraeder type valve is fitted to the expansion vessel to allow
the discharge pressure to be increased if necessary.
The expansion vessel must be charged to 0.35bar less than the
initial system design pressure.

13. Commissioning

18

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

Flue hood

Overheat

thermostat

Burner fixing screw

Combustion

chamber

cover fixing

clips (2)

Auto air
vent

Fan assembly

fixing
screws (4)

Flue Gas
Test Point

Fig. 29 - Programmer Connection - Facia Position

4

3

1

1. Programmer

2. Programmer Fixing Clip

3. Pressure Gauge

4. Programmer Connector

2

Fig. 31. Pump venting.

1

2

3

1. Electrical
Connections
Cover

2. Pump

3. Cap

Reset Button

Note: 1 bar = 10.2m = 33.5ft of water.

13.3 Set the System Pressure

Fill the system until the pressure gauge is at 2.5 bar and check
for leaks.
Release water from the system using the relief valve test knob
until the required system pressure is obtained, upto a maximum
of 1.5 bar.
Set the pointer on the pressure gauge to record the set system
pressure.
If the pressure indicated on the gauge is greater than 2.65 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 conection.
The appliance (as despatched) can accomodate a system volume
of 100 litres. Refer to BS7074 Part 1, BS5449 and table 8.
If the system volume is greater then an extra vessel must be
fitted as close as possible to the appliance central heating return
connection and pressurised to the same figure as the integral
vessel.

13.4 Clock/Programmer

The controls fitted to the appliance should be set up at this
stage.

13.5 Operation

Check that the gas and electricity supplies are turned off.
Connect a pressure gauge to the gas valve inlet and outlet
pressure test points. Refer to Fig. 33.
Set the temperature control to maximum and the clock/programmer
to operate continuously.
Turn on the gas and electricity supplies.
Turn on a hot tap to give a maximum flow rate.
A continuous spark will occur until the burner is alight and
sensed by the control circuit.
The burner will remain at its maximum domestic hot water
pressure. Refer to Table 1.
It should not be necessary for the gas valve to be adjusted. Refer
to Section 16.4.11.
Note: The burner pressure is factory set and if, after checking
that the dynamic (working) supply pressure is sufficient i.e 19-

19.5 mb approx, at the gas valve inlet pressure test point, the
correct pressure cannot be obtained then Worcester Heat
Systems Service Department should be contacted.
If the appliance does not light then check that it is not in the
'Lock-out' state by pressing the reset button. Refer to Fig. 34.
Turn off the hot tap.
The burner pressure will drop to the minimum CH setting and
will ramp up to the maximum central heating pressure.

It should not be necessary for the gas valve to be adjusted. Refer
to Section 16.4.11.
Switch the appliance off and then on to reset the control.
The burner pressure will remain at the minimum CH pressure for
a period. Refer to Table 1.
It should not be necessary for the gas valve to be adjusted. Refer
to Section 16.4.11.
Test for gas soundness at the joint between the burner and the
gas valve with leak detection fluid.

Turn the electricity supply off then back on to reset the
controls.

13.6 Domestic Hot Water

Turn the central heating temperature control knob fully anti­clockwise.
Open a hot tap near the appliance.
The burner will light and go to the maximum burner pressure
appropriate to the appliance and the gas. Refer to Table 1.
Gradually close the tap and check that the burner pressure falls.
Fully close the tap and check that the burner goes out.
The fan will continue running until the appliance has cooled to a
pre-set temperature.

13.7 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.
Check that the clock/programmer is set to operate continuously.
Set the room thermostat and the central heating control to
maximum.
The burner will light and the appliance will modulate its output
from minimum to satisfy the required heating load.
Check that all the radiators are heating up evenly.
Shut down all but one of the radiators and observe the burner
pressure fall.
Open all the radiators and check that the burner pressure rises.

19

Fig. 32. Pressure relief valve.

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

Fig. 33. Gas valve.

1

2

3

4

5

6

1 Burner pressure test point
2 Electrical connections – modulator (Blue : Blue)
3 Modulating solenoid

4 Minimum / Maximum pressure adjuster - Allen key

Note: Clockwise to increase and anti-clockwise to decrease

the pressure

5 Inlet pressure test point
6 Main gas valve connections

Max

2mm

Allen key

Min

3mm

Allen key

Gas valve
sealing
cap

13.8 Balance the system to give a temperature differential of
11°C or 13°C. A non-adjustable by-pass is fitted to the appliance.
Refer to Table 3.

13.10 Set the room thermostat to minimum and check that the
burner goes out.
Reset the room thermostat to maximum and the burner will re­light and follow the normal operating procedure.
Turn off the gas service cock.
The burner will go out but sparking from the electrode will
continue for 10 seconds when the appliance will 'Lock-out'.
After 60 seconds carefully open the gas service cock.
Switch mains electricity off and on and observe the burner re­light and follow the normal sequence of operation.
Turn off the gas service cock and electricity supply to the
appliance.
Drain the system while the appliance is hot.
Refill, vent and re-pressurise the system as described in Section

13.1 preceding, adding, if necessary, a suitable proprietary
inhibitor. Further information is available from Betz Dearborn,
0151 4209563 or Fernox 01799 550811.

13.11 Domestic Hot Water and Central heating

Set all controls to maximum.
Turn on the electricity supply to the appliance and open the gas
service cock at the appliance.
The burner will light and heat will pass into the system.
Turn on a hot tap and check that hot water is soon discharged
from the tap. Close the tap and the burner will go off.
The appliance will then return to the central heating mode and
automatically balance with the system requirements.

13.12 Completion of Commissioning

Disconnect the pressure gauge and tighten the test point screw.
Refit the cabinet.
If the appliance is to be passed over to the user immediately
then set the controls to the users requirements.
If the appliance is to be left inoperative in frosty conditions then
set the programmer, if fitted, to off.
Do not turn electricity or gas supplies off.
The appliance will operate under the control of the integral frost
protection facility.
If there is any possibility of the appliance being left totaly unused
in freezing conditions then switch off the gas and electricity
supplies and drain the appliance and system.

14.1 Tell the user how to operate the appliance and

hand over the Users Instructions leaflet.

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

14.3 Tell the user the sealed system set pressure.

14.4 Tell the user of the importance of regular servicing.

Worcester Heat Systems Ltd. offer a comprehensive maintenance
contract.

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

14.6 Complete and hand over to the user the Benchmark
Log-Book.

14. Handover

20

Fig. 34. User controls.

1

4

2

3

1 Reset Button
2 Mains Indicator
3 C.H. Temperature Control

4 System Pressure Gauge

15.1 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.

15.2 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 13.2.
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. 17 and 30.
Connect to the test point with a piece of tubing.
Expected measurements should be between:

For Natural Gas: 7.0 - 7.5% Carbon Dioxide

0.003 - 0.007% Carbon Monoxide

After taking the measurement replace the sealing cap.

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.

15.3 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. 35.
(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. 35. 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 as detailed in Section

15.3(b) above. Carefully unplug the electrical connections and
pull off the sensing tubes. Unscrew the four fixing screws and
remove the fan assembly. See Fig. 36.
(f) Combustion Chamber Front. Remove the inner casing cover.
Undo the spring clips fixing the combustion chamber front
taking care not to damage the insulation on removal. See Fig. 36.
(g) Flue Hood Assembly. Remove the fan assembly as described
in Section 15.3(e). Remove the combustion chamber front taking
care not to damage the insulation. Lift and slide the flue hood
assembly from the appliance. See Fig. 36. When refitting the hood
ensure that the rear return edge passes under the lip at the rear of the
combustion chamber.

15. Inspection And Service

21

Inner casing
cover
screws (4)

Side casing
fixing
screws (4)

Facia panel
fixing
screws (2)

Bottom
facia panel
fixing
screws (3)

Fig.35. Appliance casing and control

equipment fixings.

Fig. 36. Appliance components and fixings
(upper assembly).

1

7

5

6

4

3

2

1 Flue hood
2 Flue Gas Test Point
3 Fan assembly fixing screws (4)

4 Auto air vent
5 Burner fixing screw
6 Combustion chamber cover fixing clips (2)
7 Overheat thermostat

(h) Burner Assembly. Remove the combustion chamber front as
described in Section 15.3(f). Pull off the two spark electrode
leads, disconnect the flame sense lead at the connector and
remove the grommet. Undo the burner fixing screw. Lift up and
remove the burner assembly from the appliance. See Fig. 37

15.4 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.
Re-assemble 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.

15.5 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 13 - Commissioning.
Refit the cabinet front panel and reset the controls to the users
requirements.

16.1 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 13 - Commissioning

16.2 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 15.3. The facia panel may also need to be
hinged down as described in Section 15.3 (c).

16.3 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. 31. 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.

16.4 COMPONENT REPLACEMENT

1. Automatic Air Vent. See Fig. 36 and 38.

Remove the inner casing cover as described in Section 15.3 (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 13.2.

2. Air Pressure Switch. See Fig. 41.
Check that the electricity supply to the appliance is turned off.
Remove the cabinet front panel as described in Section 15.3 (a)
and lower the facia. Section 15.3(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. 36.
Check that the electricity supply to the appliance is turned off.
Remove the fan assembly as described in Section 15.3(e).
Fit the replacement fan in the reverse order.

4. Overheat Thermostat. See Fig. 30 and 36.
Check that the electricity supply to the appliance is turned off.
Remove the inner casing cover as described in Section 15.3 (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. 38.
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 15.3 (b, e, f and g), 15.4 and 16.4 (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.

16. Replacement Of Parts

22

Fig. 37. Burner and electrode assembly.

Spark electrode

Injector
Flame sense
electrode

Fig. 39. Spark & flame sense electrode assembly.

Open the valves and fill and re-pressurise the system as
described in Section 13.2.

6. Combustion Chamber Insulation.

Check that the electricity supply to the appliance is turned off.
If replacing the rear insulation the appliance must be drained as
described in Section 16.3(a) and 16.3(b) and the gas to water
heat exchanger removed (see 16.4.5).
If changing the front or side pieces it is not necessary to drain
the appliance.
Remove the inner casing cover, combustion chamber front, fan
and flue hood assembly as described in Sections 15.3 (b,e,f & g).
Remove the fibre insulation pads to be changed and fit the
replacements taking care not to damage them.
If the system has been drained, open the valves and fill and re­pressurise the system as described in Section 13.2.

7. Burner. See Fig. 37.
Check that the electricity and gas supplies to the appliance are turned off.
Remove the burner assembly as described in Section 15.3 (h).
Fit the replacement burner in the reverse order taking care not to
damage the electrode leads.

8. Burner Injector. See Fig. 37.
Remove the burner as described in Section 15.3 (h).
Unscrew the brass injector from the manifold.
Fit the replacement injector in the reverse order.

9. Spark Electrode Assembly. See Fig. 39.
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. 39.
Remove the burner as described in section 15.3(h).
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 40.
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 15.3(c).
Note: The adjuster sealing cap should be fitted after setting the
burner pressure and coated with a small amount of paint to
make any subsequent adjustment obvious.
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. 40.
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.

23

3.5-4.5mm

2.5-5mm

Fig. 38. Combustion chamber.

Heat
exchanger

Overheat
Thermostat

Hot water
connections

Cut-outs in
combustion
chamber sides

Pump bulk-head
connector

Central heating
connections

Auto air
vent

Flame Sense Electrode

Spark Electrode Assembly Burner

Spark electrode
assembly from side
and above

Flame sense electrode
detail

5-6mm

Fig. 40. Gas valve.

1

2

3

4

5

6

1 Burner pressure test point
2 Electrical connections – modulator (Blue : Blue)
3 Modulating solenoid

4 Minimum / Maximum pressure adjuster - Allen key

Note: Clockwise to increase and anti-clockwise to decrease

the pressure

5 Inlet pressure test point
6 Main gas valve connections

Min

3mm

Allen Key

Max

2mm
Allen

Key

Gas valve
sealing cap

To set the burner pressure. See Fig. 40.
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 13.6. - Appliance Operation.
Adjust the maximum pressure adjustment (2mm Allen screw on
the gas valve) to give a burner pressure of 13.5 mbar on natural
gas. 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).
Open a hot tap.
Remove one of the blue leads from the modulating solenoid on
the gas valve to ensure that the burner pressure remains at the
minimum setting. See Fig. 40.
Adjust the minimum pressure to 1 mbar using a 3mm Allen key.
Replace the blue lead and re-check the pressures.
After completing the adjustments, check the minimum and
maximum pressures and re-adjust as necessary.

Re-fit the adjuster sealing cap and coat with a small amount
of paint to seal the cap to make any subsequent adjustment
obvious.

12. Central Heating Sensor. See Fig. 41.

Check that the electricity supply to the appliance is turned off.
Hinge the facia assembly in the servicing position as described in
Section 15.3(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.

13. Domestic Hot Water Sensor. See Fig. 41.
Check that the electricity supply to the appliance is turned off.
Hinge the facia assembly in the servicing position as described in
Section 15.3(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 Fig. 41.
Check that the electricity supply to the appliance is turned off.
Drain the central heating circuit as described in Section 16.3(a).
Hinge the facia assembly in the servicing position as described in
Section 15.3(c).
Remove the burner assembly as described in Section 15.3(h).
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 13.2
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 16.3(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 16.3(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 13.3

16. Pressure Relief Valve. See Fig. 41 and 42.
Drain the central heating circuit as described in Section 16.3(a).
Hinge down the facia assembly as described in Section 15.3(c).
Remove the Bottom panel as described in Section 15..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 13.3.

17. Water Flow Turbine. See Fig. 41 and 43.
Check that the electricity supply to the appliance is turned off.
Drain the domestic hot water circuit as described in Section

16.3(b).
Remove the two upper screws and hinge down the facia panel as
described in Section 15.3(c).
Disconnect the electrical connection.

Unscrew the securing nuts and remove the turbine housing from
the pipework.

Fit the replacement water flow turbine in the reverse order
ensuring new fibre washers are fitted to the new turbine body.
Check that the correct, blue, flow restrictor is fitted.

NOTE: Washers are different

Inlet = Outlet =

24

Fig. 41. Appliance Components
(Lower Assembly)

1 Pressure relief valve
2 Domestic hot water sensor
3 Water flow turbine
4 Gas valve
5 Pump
6 Air pressure switch
7 Air pressure switch connecting tubes
8 Pressure gauge connection
9 Gas valve electrical connections
10 By-pass pipe
11 Fixing disc and screw
12 Central heating sensor

4 5 6

1

2 3

98

7

1110

12

19. Pressure Gauge. See Fig. 34.
Check that the electricity supply to the appliance is turned off.
Drain the central heating circuit as described in Section 16.3(a).
Remove the two upper screws and hinge down the facia panel as
described in Section 15.3(c).
Prise back the retaining clips securing the gauge to the facia
panel. Unscrew the fixing disk 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 13.3.

20. Control Board. See Fig. 44.
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 unscrew the earth lead from the left and
side panel.

Remove the four corner screws on the rear of the facia and
separate the metal back panel from the plastic facia.
Remove the flame sense and ignitor leads from the control board.
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 15.3 (c).

21. Gauze Filter. See Fig. 45.
Remove the water flow turbine as described in section 16.4-17.
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 using a new
fibre washer.

25

Fig. 43. Water Flow turbine.

1

1 Flow turbine
2 Flow restrictor (10l Blue)
3 Fibre washer (inlet)
4 Electrical connection
5 Direction of flow
6 Fibre washer (outlet)

Fig. 42. Pressure relief valve.

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

2

6

5

3

4

Fig. 44. Control board.

Fig. 45. Gauze Filter.

Gauze Filter

Isolating Valve

1 Facia
2 Control board
3 Rear cover
4 Fixing screws

4

3

2

1

Type

Type

Fibre Washer

22. Flue flow sensor. See Fig. 46.
Check that the electricity supply to the appliance is turned off.
Remove the fan assembly as described in Section 15.3(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.

26

Positive

Fig. 46. Flue flow sensor.

27

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 6°C

above set point

Operating Switch

(or programmer)

OFF

Continue

pump and fan

for 4 mins plus

extra 4 mins

pump.

Gas valve OFF

Room thermostat

OFF

Burner pressure

CH min (1.5 mbar )

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

28

Signal from the

flow turbine

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 1.5 mbar

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 55°C

No demand and central

heating temperature above

50°C monitored by the

central heating sensor

End of demand or central

heating temperature above

70°C monitored by the

central heating sensor

Pump and 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 flow

greater than

2.9 l/min

Gas valve OFF.

Fan remains ON

Modulate heat

input to maintain

hot water

temperature at the

factory pre-set

level

Gas valve OFF

Operating

Switch (or

programmer

OFF)

Domestic hot water

temperature

monitored by hot

water sensor

3. "Autofrostat" Function

4. Pump Overrun Function

5. Over run Function

2. Domestic Hot Water Mode

6. Central Heating ramp control

Flow less than

3.5 l/min

min burner pressure

Flow <2.7 l/min

gas valve off

If burner on less than

3 min;

10 sec pump and fan

over-run

If burner on more than

3 min;

10 sec over-run

80 sec fan over run

10 sec pump over run

80 sec fan over run

Pump on

for

4 minutes

29

F1 2A

F2 1AT

Optional links

Spark

Flame sense

Outputs Inputs

Mains
indicator

Modulating

valve

Overheat stat

X6 Pins 8 & 9

X6 Pins 15 & 16

X6 Pins 5,6 & 7

X6 Pins 14, 17 & 18

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 1

X4 Pin 1

FAN

PUMP

RL3

RL4

N

N

N

N

L

18. Fault Finding

Note: This fault-finding information is for guidance only. Worcester Heat Systems cannot be held responsible for costs incurred by
persons not deemed to be competent.

PRELIMINARY CHECKS

Preliminary electrical system checks are the first electrical checks to be carried out during a fault-finding procedure. On completion of
the Service/Fault-Finding task which has required the breaking and remaking of electrical connections, check (a) EARTH CONTINUITY,
(b) SHORT CIRCUIT CHECK, (c) POLARITY and (d) RESISTANCE TO EARTH.

30

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

31

No mains LED

Connect mains

supply

Replace fuseIs Fuse F1 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

32

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

33

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

34

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

35

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

It is not possible to

seperately test the gas

valve and the supply

lead.

Relpace the gas valve or

the lead.

Is live output present at

X5 pins 1 & 2 relative to

neutral at pin 3?

Note: Readings to be

taken within 9 seconds

of a demand.

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?

36

Is minimum pressure

observed at burner at all

times?

Modulating Valve Check

Flow turbine Check

GO TO

CHECK I

YES

YES

YES

YES

NO

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

Does the boiler ignite
at a higher flow rate?

Faulty turbine.

Replace.

Faulty PCB.

Replace

Disconnect the 3 way in-line

connector.

Check that there is 5V DC output

from the PCB at the connector.

Red +5V Black 0V

Faulty modulating valve .

Replace gas valve

Remove X6, measure

resistance between

pins 15 & 16

N

YES

NO

O

Re-connect the 3 way connector

and open a tap to run the turbine.

Check that there is between 1.5 and

4.5 V DC across the green and black
wires/terminals.

With boiler cold, slowly open HW

tap. When flow reaches 3l/min
does boiler ignite? (Flow can be

checked using a measuring jug and

stop watch)

YES

NO

GO TO

CHECK I

HARNESS OK

YES

Faulty turbine.

Replace

Turbine OK

NO

NO

1 Burner Assembly Natural Gas Aeromatic AC 23/053595 1 8 716 142 652 0
2 Injector Natural Gas Stereomatic O 4.5mm 1 8 716 140 208 0
3 E01-892 Gas valve Natural Gas Dungs BM771 1 8 716 150 766 0
4 Air Pressure Switch Huba 605.99530 1 8 716 146 159 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 Buccleuch 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 Giannoni 1 8 716 142 905 0
9 E01-600 Insulation Pack WHS 1 8 716 192 216 0

10 E01-601 Auto Air Vent Intermes 1 8 716 140 5040

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 Winkelman Panhof (8Ltr) 389mm Dia 1 8 716 142 502 0
15 E58-079 PCB Boiler Control Pactrol 423100 1 8 716 146 329 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 Blue 1 8 716 141 052 0
19 324-822 Gauze Filter WHS 1 8 716 148 401 0
20 Flow Turbine SIKA VTY 1 8 716 146 160 0
21 Fan Assembly FIME 1 8 716 121 681 0
22 E01-607 Overheat Thermostat Ranco LM7 1 8 716 142 307 0
23 299 357 Fuse Pack WHS 1 7 716 192 206 0
24 E01-610 Gasket Pack WHS 1 7 716 192 281 0

ACCESSORIES

299-360 Mechanical Programmer Kit DIEHL 7 716 192 002

E05-341 Mini Expansion Vessel Kit Including new pipe and Expansion Vessel 7 716 192 188

FLUE OPTIONS

Telescopic Horizontal Flue Kit 425 - 725mm 7 716 191 068
E01-943 Extension Flue Kit 750mm 7 716 191 006
E01-944 Vertical Flue Kit 7 716 191 069
E01-945 Vertical Flue Adaptor 7 716 191 016
E01-946 Internal Fixing Kit Telescopic Flue 7 716 191 019
E01-058 Flue Elbow Kit 90 deg. 7 716 191 013
E01-059 Flue Elbow Kit 45 deg. 7 716 191 014

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

37

19. Component Parts List

38

9

24 23

20

3

5

8

14

12

13

10

3

21

1

15

22

4

11

23

20

7

6

25 24

2

19

18

16

39

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 8 716 114 751a (11/07)

Worcester Heat Systems Limited (Bosch Group), Cotswold Way, Warndon, Worcester WR4 9SW.

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

Technical Helpline [phone].

www.worcester-bosch.co.uk

This manual is to be used in conjunction
with the variant part number of the bar
code below: