MHS Boilers EURON 24, EURON 24 HG, EURON 30 HG, EURON 30 HSG Installation Manual

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Installation and Operation
Guide

EURON 24/30HG

EURON 30 HSG

Manual Ref: L307

2 of 49

Contents ......................................................................... 2

General Information ......................................................................... 3

Regulations ......................................................................... 3

Conditions of warranty ......................................................................... 3

Quality of heating circuit water ......................................................................... 4

 5

Technical Data .................................................. 6 - 7

Dimensions ....................................................... 8

Minimum clearances ........................................ 9

Connection Kits ................................................ 10

Access to Boiler / Case removal ....................... 11

Connections ..................................................... 12

 13

Ciculation Pump ............................................... 14

Electrical Connections .................................... 15 - 16

Connection of air/flue gas pipes ....................... 17

Air/flue gas routing ........................................... 18

Flue variants and dimensioning ....................... 19

Commissioning Preparation for operation / Control Panel ......... 21 - 22

Parameter adjustment to control unit QAA73 . . 23

Flue gas Measurement and Adjustment ........... 24 - 27

Safety check of heating appliance .................... 28

Parameters ....................................................... 29

Gas Changeover ............................................... 30 - 32

Service and Maintenance Monitoring and checks ...................................... 33 - 34

Error Indication ................................................. 35 - 36

Service Access to Boiler / Cover Removal ....... 37

Dismantling burner and heat exchanger ........... 38

Service Requirments ........................................ 46

Appendix QAA 73  End User Parameters ...................... 40

QAA 73  Engineer Parameters ........................ 41

LMU 54  Engineer Parameters ........................ 42

LMU 54  Specialist Engineer Parameters ....... 43 - 44

Flue Termination Guidlines ............................... 45

Typical Hydraulic Schemes ............................... 46

Notes ......................................................................... 47

Contents

3 of 49

General Information, Regulations
Conditions of warranty

General Information

Installation, assembly, gas
connection, electrical connection and
first commissioning must be carried
out by, and is the responsibility of, a
competent specialist(s).

Operator/End user Information

To ensure the continuing safety,
reliability and efficient functioning of
the boiler, the equipment must be
regularly serviced by a competent
specialist.

To ensure regular and essential
Servicing and Maintenance we would
recommend entering into a Service
Contract (Please contact MHS Boilers
Service Department for more details)

Clarification of Warranty
conditions

Faults arising from the following are
excluded from our warranty:

- Inappropriate or incorrect use

- incorrect installation i.e. not as per
MHS installation requirements

- Commissioning not carried out by
MHS  Parts Only Warranty

- use of non-genuine spare parts

- Poor system water quality and
failure to maintain water treatment

- Use of inappropriate fuel

- Operation of boiler with excessive
or insufficient water pressure

- Operation of boiler using incorrect
power ratings

- Unauthorised modification or
alteration

- Failure to observe the information
in the manual and the instruction
plate on the burner equipment

Instructions, data badge and warning
labels on the boiler must never be
removed or altered. If damaged or
missing should be replaced as soon as
possible.

This appliance manual must be
handed to, and left with, the end
user following successful
completion of the installation.

This appliance should never be left
to operate with the outer casing
removed

Regulations and Standards

For safe, environmentally sustainable
and energy saving operation, observe
the following standards:

BS 5440-1:2008 Flueing and
ventilation for gas appliances of
rated input not exceeding 70 kW
net. Specification for installation of gas

appliances to chimneys and for
maintenance of chimneys

BS 5440-2:2000 Flueing and
ventilation for gas appliances of
rated input not exceeding 70 kW
net. Specification for installation and

maintenance of ventilation for gas
appliances.

BS 5449: Part 1 1977 Code of practice
for central heating for domestic
premises

BS 6798:2000 Specification for
installation of gas fired boilers of rated
input not exceeding 70 kW net.

BS 7671. Requirements for electrical
installations. IEE wiring regulations.

BS EN 12828: 2003 Heating systems

in buildings. Design for water-based
heating systems

Water Regulations (Water Fittings)
Regulations 1999.
Gas Safety (Installation & Use)
Regulations 1998.

4 of 49

Heating circuit water quality

Heating circuit water quality

The composition and quality of the
system water have a direct influence on
the performance of the whole system
and the life of the boiler. On first filling,
and any subsequent refilling, a pH
balance of 7-8 should be maintained.
Please see the table below

The system must be flushed, cleansed
and treated with a good quality
corrosion inhibitor suitable for all the
materials in the system before the
boiler is put into use.

Failure to do this may affect the
boilers warranty.

No Chemical anti-corrosion medium
should be introduced to the system

Recommended Water treatment
Specialists:

Fernox
Forsyth Road
Sheerwater
Woking
Surrey
GU21 5RZ

www.fernox.com

Office Tel: [phone]
Technical Support: 0870 870 0362

Criterion

Appropriate Value

Effect of Deviation

PH - balance

7 - 8

Danger of corrosion for boiler and system
components.

Hardness

14dH

- Raised calcium deposits

- Low life expectancy of boiler

Chloride content

150 mg/l

Corrosion of alloyed materials

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Product Description
Overview

EURON HG

Legend

1 Air intake openings
2 Concentric air intake/flue gas connection
3 Manual air vent
4 Flue gas discharge / Flue hood
5 Burner Door / Burner
6 Stainless steel heat exchanger
7 Condensate drain hose
8 NTC Return sensor
9 NTC Flow Sensor
10 Condensate discharge Siphon
11 Low water pressure switch
12 Supply air hose
13 Heating system pressure gauge
14 Pump
15 Gas valve
16 Premix air/gas burner supply tube
17 Modulating burner fan
18 Ionisation electrode
19 Ignition electrode
20 Ignition transformer
21 STB flue gas 85 °C

22 Air/flue gas sampling points

EURON 30 HSG Combi

Legend

1 Air intake openings
2 Concentric air intake/flue gas connection
3 Manual air vent

4 Flue gas discharge connection
5 Burner
6 Stainless steel heat exchanger
7 Condensation drain hose
8 NTC Flow sensor
9 NTC Return sensor
10 3 way diverter valve
11 Condensate discharge Siphon
12 NTC domestic water sensor
13 Low water pressure switch
14 Supply air hose
15 Domestic hot water plate heat exchanger
16 Cold water inlet with filter
17 Hot water flow regulator
18 Heating system manometer
19 Pump
20 Gas valve
21 Premix air/gas burner supply tube
22 Modulating burner fan
23 Ionisation electrode
24 Ignition electrode
25 Ignition transformer
26 STB flue gas 85 °C
27 Air/flue gas sampling point

Euron 30 HSG

6 of 49

Product Description

Technical Data – System Boiler

Units

HG 24

HG 30

Nominal Heat Output at 80° / 60° C

kW

5,8-22,8

6,9-28,1

Nominal Heat Output at 50° / 30° C

kW

6,1-23,6

7,2-29,2

Nominal Heat Input

kW

6,0-23,0

7,1-28,5

Normal supply level 75° / 60°C

%

107,2

107,1

Normal supply level 40° / 30°C

%

108,6

108,5

Standby loss TK = 70°C

%

0,1

0,1

Max. output pressure of Fan

Pa

110

90

Water content L 1,8

2.5

Max. water pressure

bar

3.0

3.0

Max. flow temperature

°C

82

82

Condensate quantity at 40° / 30°C (22 kW)

ca. l/h

1,58

2,95

Gas Flow rate: Natural Gas G20

m3/h

2,43

3,01

Liquid Propane Gas LPG / G31

kg/h

1,81

2,25

Gas flow pressure: Nominal

mbar

20 Natural Gas
50 LPG

Gas flow pressure: min / max.

mbar

18 / 25 Natural Gas
50 LPG

Flue gas mass flow rate with Natural gas

g/s

10,19

12,47

Max Flue gas temperature

°C

74

71

Gas category

112H3B/P; 112E3P

Flue Classification

(B23 C13x C33x C43x C53x C63x C83x)

Electrical protection rating

IPX4D

NOx

Class 5

Ionisation min

uA

1

1

Connections: Air/flue gas hose

DN

80/125

80/125

Heating Flow / Return

mm

22

22

Gas connection

DN

3/4"

3/4"

Condensate hose connection

mm

28

28

pH balance - condensate

pH

3,2

3,2

Electrical Power consumption 230 V / VAC

W

129

129

CE - Identification number

0085BP0033

Width x height x depth

mm

450 x 750 x 378

Weight ca.

kg

35

37

Noise level Min./Max. load

dB (A)

36 -44

Product variables in calculating installation costs
according to DIN V4701-10:

Rated heat capacity



22,8

28,1

Efficiency at rated heat capacity



98,4

97,8

Part load efficiency

h

3

o% (%)

107,8

107,4

Return temp, on measurement of 30% part load efficiency

T 30% (C)

30

30

Standby heat loss

q B.70 (%)

2,6

2,2

Electrical Consumption Max

W

129

129

7 of 49

Product Description

Technical Data – Combi Boiler

Units

HSG 30 Combi

Nominal Heat Output at 80° / 60° C

kW

6,9-28,1

Nominal Heat Output at 50° / 30° C

kW

7,2-29,2

Nominal Heat Input

kW

7,1-28,5

Normal supply level 75° / 60°C

%

107,1

Normal supply level 40° / 30°C

%

108,5

Standby loss TK = 70°C % 0,1

Max. output pressure of Fan

Pa

90

Service water temperature max./min.

°C

60/35

Hot water quantity AT=40°C

l/min./60°C

10,0

Minimum HWS Flow rate

l/min./60°C

2,5

Service water pressure max./min.

bar

6/0,8

Water content

I

2,5

max. water pressure

bar

3.0

max. flow temperature

°C

82

Condensate quantity at 40° / 30°C (22 kW)

ca. l/h

2,95

Gas Flow Rate: Natural Gas G20

m3/h

3,01

Liquid Propane Gas LPG / G31

Kg/h

2,25

Gas flow pressure norm

mbar

20 Natural Gas
50 LPG

Gas flow pressure min./max.

mbar

18 / 25 Natural Gas
50 LPG

Flue gas mass flow rate with Natural gas

g/s

12,47

Max Flue gas temperature

°C

71

Gas category

112H3B/P; 112E3P

Flue Classification

(B23 C13x C33x C43x C53x C63x C83x)

Electrical protection rating

IPX4D

NOx

Class 5

Ionisation flow min.

uA

1

Connections: Air/flue gas hose

DN

80/125

Heating Flow / Return

mm

22

Gas connection

DN

3/4"

Condensate hose connection

mm

28

pH balance - Condensate

pH

3,2

Electrical Power consumption 230 V / VAC

W

129

CE - identification number

0085BP0033

Width x Height x Depth

mm

450 x 750 x 378

Weight ca.

kg

37

Noise level Min./Max. load

dB (A)

36  44

Product variables in calculating Installation
costs according to DIN V4701-10:

Rated heat capacity



28,1

Efficiency at rated heat capacity

hioo% (%)

97,8

Part load efficiency

h

3

o% (%)

107,4

Return temp.on measurement of 30% part load efficiency

T 30% (C)

30

Standby heat loss

q B.70 (%)

2,2

Electrical Consumption max W 129

8 of 49

Product description
Dimensions

EURON24HG EURON 30 HG
Legend

A Flow 3/4"
C Gas inlet 3/4"

E Return 3/4"

G Condensation discharge 28 mm

H Siphon

(*) Water connection
(**) Gas connection

EURON 24 HSG Combi
EURON 30 HSG Combi

Legend

A Flow 3/4"

B Hot water outlet 1/2"

C Gas inlet 3/4"

D Cold water inlet1/2"
E Return 3/4"

G Condensation discharge 28 mm

H Siphon

(*) Water connection
(**) Gas connection

9 of 49

Installation

Minimum clearances

Minimum clearances

For servicing of Boiler the

minimum clearances specified in the
diagram must be observed.

Wall mounting

Fix to the wall using the mounting
bracket and fixings supplied.

10 of 49

Installation

Connection Kits

Connection Kit.

Each boiler comes with a connection
kit for gas, flow and return connections
on the system boiler and gas, flow,
return and Hot water service
connections for the Combi boiler.

These kits are there to aid installation
and remove the need for the installer

to provide isolation valves for the boiler

System Boiler Connection Kit

Combi Boiler Connection Kit

Important Note:

The Gas Isolation Valve, that is included as part of the connection bracket assembly (for Boiler
versions),  device.

The slam shut action of the valve is activated at 100ºC +/- 5K.
Installers should therefore avoid the use of soldered fittings in the gas line which are in close
proximity to the gas isolation valve.

If a fault occurs that indicates that no gas is able to pass through an isolation valve, then it should be
suspected that the thermal shut-off feature has been triggered. There is no possibility to reset a
triggered valve and it must be replaced.

11 of 49

Installation

Access for Installation /Commissioning/ Servicing/Maintenence

Access to the Boiler is as follows:
Ensure boiler is switched off at the mains and Isolated from gas supply
Then to gain access to inside the boiler, complete the following steps:

Remove the 4 screws (1) from the
underside of the housing (2 either
side)

Open the Release clips on top of the
boiler Casing

Pull the Boiler casing towards you.
You will now have acces to the
internal components of the boiler

Hinge forward the Control panel (4) for access to the rear of the controller
and wiring. Removing the 5 screws (5) will enable the rear cover (6) to be
removed for access to wiring.

1 1 2

3

240v Connections

Low Voltage
Connections

12 of 49

Installation

Connections

Gas connection

The Boiler is designed to belong to
the following categories for the use of
gas types.

Country

Categories

GB

II2H3P
II2H3B/P

Please check the Boiler name plate and
packaging to ensure that it is correct for
UK Operation and that the gas category
corresponds to one of the appropriate for
the UK.

The gas inlet must be manufactured and
measured according to the relevant
specific country regulations as well as the
maximum output of the equipment; check
also the correct calculation and
connection of the stop valve.

Before installation, the gas line should be
thoroughly cleaned, so that any residue
does not impair the functional efficiency
of the heating appliance.

Also ensure that the boiler is for the
correct type of gas to be used i.e. Natural
Gas or LPG (check the name plate in the
interior of the appliance).

Check the required gas pressure for
either natural gas or LPG.

Water connection

All connections for water and gas are
as per the illustration on page 8.
Ensure that the cold water main
pressure does not exceed 6 bar. If > 6
bar then a pressure limiter device must
be fitted.

The minimum pressure needed by the
appropriate devices for processing of
hot service water is about 0.2 bar.

On sizing the pipes and the heating
element of the Boiler, the residual
head pressure must be considered
depending on the required flow rate as
per the pump circulation curve (see
page 14)

With Combi Boiler (type HSG) flow
limiters are built into the water switch.
This ensures a constant flow of service
water

(EURON 24 HSG = 8 Litre/Minute
EURON 30 HSG = 10 Litre/Minute).

Underfloor heating

For underfloor heating, attach a
suitable safety thermostat to the
supply. (see page 15)

Note: High flow temperature leads to
an operating lockout of the Boiler both
in DHW and heating operation:
The error code "110" appears on the
display. Operation is resumed by
pressing RESET (6) key (see page 22),
after the flow temperature has
dropped.

13 of 49

Installation

Hydraulic diagrams

EURON HG/HSG
Legend

1 Manual bleed valve
2 Stainless steel heat exchanger
3 Burner
4 Mixing channel air/gas
5 Modulating Fan
6 Venturi

7 Gas valve

8 NTC-Appliance supply sensor
9 Motor of 3-way valve (Combi)
10 3-way valve (Combi)
11 Minimum pressure switch
12 NTC-Service water sensor (Combi)
13 Service water plate heat

exchanger (Combi)
14 Service water flow control (Combi)
15 Cold water filter (Combi)
16 Automatic heating bypass
17 3 bar safety valve
18 Pressure Gauge
19 Circulation pump
20 Automatic bleed valve
21 Condensate syphon
22 NTC-appliance return sensor
23 Flue Gas Collection Hood
24 Expansion tank (optional)
25 Flue Gas STB

A Flow 3/4"

B Hot water outlet 1/2" (Combi)

C Gas intake 3/4"

D Cold water intake1/2" (Combi)
E Return 3/4"

EURON HG

EURON HSG

14 of 49

Installation

Circulation pump

Residual head pressure of the circulation pump at pump speed 2 + 3

24 HG

30 HSG/HG

Flow rate

V3

(mbar)

V2
(mbar)

V3

(mbar)

V2
(mbar)

1300

1200

127,5

1100

162,5

119

1000

221 190 900

280

83

252 800

325

142,5

308

102

700

373,5

207

361

165

600

419,5

269

409

231

500

459,5

320

463

287

400

491,5

365

503

343

300

522

408,5

548

394

200

547

440

561

440

100

568

470

588

467

0

584

494

601

491

Legend
V2 2. Pump stages

V3 3. Pump stages

Graphic representation of the residual head pressure of the circulation pump at pump speed 2 + 3 (please note that this graph
includes models not covered by this manual)

Stage 3

Stage 2

15 of 49

Installation

Electrical connections

General Information

Electrical installation and connection
must be carried out by an authorised
installer in accordance with applicable
National Standards, Local Standards
and Regulations.

Mains connection and Customer
wiring

The appliance is designed for
permanent connection using cables
NYM 3x1.5 mm2 or H05W-F 3 x 1
mm2. The connection cable should not
be larger than 8 mm in diameter.

Connect the mains wiring to the
respective terminals, on the Boiler
Terminal strip, in the 240V section at
the rear of the control panel. (See
picture below)

A suitable mains isolator switch must
be fitted in the power supply, to the
boiler, and sited in the boiler room.
This can be used to switch off power
to the boiler for maintenance purposes
or in the event of a problem.

Mains voltage: 230 V, 50 Hz

Mains cable Connection

All external connection cables should
be stripped to a max. 30 mm. All
external Cables entering the Boiler
must be firmly clamped in the Cable
grip after connection

The length of the cables must be
designed accordingly. Additional
cables (e.g. for system integrations),
which are attached to the terminal strip
in the boiler, must be secured along
with mains lead via the Cable grip.

When connecting the boiler, ensure
the earth cable (yellow/green), which
is longer than the supply wires (see
illustration) is connected.

Multiple plug sockets, extension cable
and adapter are not appropriate. For
earthing of the appliance under no
circumstances use the piping of the
water supply installation, heating or
gas installation.

Please note the appliance is not
protected against damage from
lightning strikes.

If the mains fuses are to be changed,
use 2A Quick Blow fuses.

Note before any connections are
made below the boiler must be
switched Off.

Remote Operation (Volt Free)

A volt free enable to the Boiler for a
Thermostat, Time switch etc, is
possible via X10-02 (2)

Remote Operation (QAA73)

Connection (1) for a QAA73 must

be via a cable with at least. 2 x 0,5

mm2.

The "Bus" cable of the QAA73

(20-30 V) must be installed and

run separately from the 230 V/50

Hz cables. The QAA73 connects

to the X10-01 connector using

screened cable.

Note: If the QAA 73 remote

control is being used, the

thermostat bridge must be

disconnected from the X10-02 (2)

connection.

Note: Only one type of Boiler
enable can be used via either
X10-01 or X10-02

Ambient / External Sensor
(QAC34)

Connect the Outside Air
Temperature sensor (3), if
required, using a Screened Cable
with at least 2 x 0,5 mm2, with a
maximum length of 50m.

The sensor should be positioned
on a North Facing Wall at a height
of 2 2.5 m above the floor. Under
no circumstances must it be
directly exposed to sunlight.

Connect the ambient/external
sensor to the X10-06 (3)
connector (using screened cable).

Safety Thermostat for
Underfloor Heating

Remove the bridge loop from the
terminals on the right hand side of
the Terminal Block, on the 240v
connection side, and connect the
safety thermostat for the
underfloor heating.

The Connections on the boiler
wiring side will be pre-wired back
to X3-01 on the LMU unit.

Earth Block

240v Mains Power Connection

240V Connection.
1st TwoTerminals

Connection for
Underfloor limit
thermostat

Cable Grip

16 of 49

Installation

Electrical connections

Controls Options / Accessories

OCI420 Clip in Module - For Multiple Boiler communication.
AGU2.514 Clip in Module  For system incorporating pumped Heating circuit & Pumped HWS Primary (see P46  scheme 1)
AGU2.511 Clip in Module  BMS Run / Fault Indication & 0 -10v input Clip
RVA47 Cascade Control - Cascade Controller for multiple boiler applications
RVA46 Zone Control
RVA63 Multi Zone Control

17 of 49

Installation

General
Connection of air/flue gas pipes

Flue gas and supply air connection

The EURON is suitable for use as
conventional or balanced Flue. The
flue that is connected must be
removable.

As with all flue systems, it must be
ensured that there is no short circuit /
cross-contamination between the
supply air and flue gas.

For flue gas safety the EURON is
fitted with an flue gas temperature
safety limiter (set at 85°C), therefore
this does not need to be provided for
in the installation.

The combustion air supply must be
ensured. In areas such as in a laundry
or workshop, a hair salon, in areas with
electroplating,printing or metalworking.
In such or similar cases the supply air
must be supplied from a outside the
building.

Condensate connection

For every m3 of natural gas burnt, 0.7
to 1.0 litres of condensate is produced,
as a consequence of the very high
utilisation of energy. This of course
must be discharged from the boiler.
Due to its acidic nature, plastic piping
must be used for draining the
condense. The condensate must be
able to run off freely into a tundish (or
neutralization tank), therefore avoiding
a back-up of condensate into the
boiler. Please Refer to BS6798:2000
for guidance.
(See picture to right)

Condensate created in the flue must

also be allowed to drain away freely
with the same considerations as for
the boiler condesate. Local regulations
must be observed. Prior to
commissioning the siphon in the
EURON must be filled with water .

Connection to air/flue gas routing

For concentric air/flue gas routing only
original MHS accessory parts should
be used.

Condense
Connection

18 of 49

Installation

Air-flue gas Installation

For the installation of concentric
air/flue gas systems the use of
original accessory parts by MHS is
recommended.

Connection kits for fluing of the air/
flue gas are supplied separately from
the appliance depending on the
various installation options.

This boiler comes ready for
connection to a concentric air/flue gas
system.
The flue connection to the boiler can
be either using 80/125mm concentric
flue or via double pipe 80/80mm flue.

19 of 49

Installation

Air/flue gas Installation

Combustion Air from the Boiler Room, Ø 80mm PPS

B23

Open Flue Appliance – Air Supply fgrom the room – Flue Gas discharge via
roof.

Room Sealed Appliance, Ø 80/125mm PPS / Alu

C13

Room sealed appliance – Connected to Concentric supply / flue discharge
through a wall

C33

Roome Sealed appliance – connected to concentric air supply / flue
discharge through the roof

C43

Room Sealed appliances, connected in cascade, connected to a common U
shaped concentric supply / flue discharge at the appliance

C53

Room sealed appliance, connected to a separate air supply and flue
discharge pipe, opening into different pressure areas.

C63

Room sealed appliance, sold without related connecting and/or discharge
fittings.

C83

Room sealed appliances in cascade, connected to separate air supplies
but common flue discharge through the roof.

Note: For Flue Gas Termination Guidance please refer to the diagram on page 44

20 of 49

Condense Connection

Commissioning

Preparation for operation

General

To ensure the safe and correct operation
of the boiler, commissioning must be
carried out by a suitably qualified
specialist.

Monitoring

Ensure condensate connection is
connected using the condense drain
hose supplied or using plastic piping.
Ensure that the Condense outlet is
piped to a suitable drain. Please refer to
BS6798 for ultimate guidance

First commissioning
Fill hydraulic circuits

Proceed as follows:

Open the boiler bleed valve and the
valve above the stainless steel heat
exchanger.
Loosen the closure of the automatic
bleed valve on the circulation pump.
Slowly open the system filling point
and shut the bleed valve on the
stainless steel heat exchanger, and
the boiler, as soon as water is
evident. Shut the filler valve, once
the pressure shown on the water
pressure gauge reaches 1.0 bar.

Ensure that:

The the automatic bleed valve on
the circulation pump is opened.
The boiler pressure, on the
manometer is 1 bar. The gas valve
is completely shut off. The electrical
connection has been correctly
made.

Ensure in every case, that the
green/yellow earth wire is connected to
a suitable earth.

To bleed the appliance, proceed as
follows:

Switch on boiler (10). This sets the
pump of the heating appliance in
operation and there are three
consecutive attempts to ignite the
burner. After the third attempt the
electronics lock the appliance, as
the gas supply is cut; the display
shows the readout "133".
Allow the pump to work until all the
air has left the appliance. Vent the
boiler. Check the appliance
pressure and refill with water in the
case of a drop in pressure, until
pressure again reaches 1 bar.

Check the flue gas system.

Ensure that any necessary room
ventilation openings are open.
Ensure the boiler condensation
siphon is filled with water.

(See illustration below centre).
If the appliance is unused for a long

period, the siphon must be filled
before switching on again. It is
dangerous not to refill the siphon with
water, as this can cause the flue gas
to escape from the condense drain.

Open the gas tap and check the
tightness of all connections. Unlock
the boiler by pressing the Reset key
"6". The burner will ignite. Should this
not happen, repeat the above
procedure, until the burner ignites.

Gas supply

Proceed as follows:

Ensure that the type of gas used
corresponds to the type of gas
indicated on the nameplate of the
boiler.

Power supply

Ensure that the voltage and frequency
of the power supply conform to the
data on the name plate of the boiler.

Ensure that the live and neutral
connections have been made and to
the correct terminals. Check that the
earth is connected.

21 of 49

Commissioning

Preparation for operation

Legend

1 Display
2 LED (green) Burner operation
3 LED (red) Alarm appliance

lock

4 LED (green) flow temperature

readout on display

5 LED (green) operating

phase/diagnosis of Boiler
6 Reset Button
7 Display adjustment Button
8 Flue cleaner function Button
9 Summer/winter/automatic

operation Button
10 Power on/off
11 Hot water temperature

Adjustment
12 Heating flow temperature

Adjustment
13 LED illuminates winter

operation
14 LED (green) automatic Boiler

operation

Commissioning

Switch on the POWER (10)  0 = Off;
1 = On 1. The display will illuminate,
then after a few seconds the heating
appliance is ready to operate.

Winter and summer operation

Use MODE (9) button to change
changed between winter and summer
operation and vice versa. When LED
(13) is illuminated the boiler is on
winter operation.
If an outside air temperature sensor is
fitted to the boiler, the changeover
from winter operation (heating and hot
service water) to summer operation
(only hot service water) can occur
automatically, if the outside
temperature measured is higher than
20 °C.

This can be achieved by pressing the
MODE Button (9), until the LED AUTO
(14) is illuminated. To deactivate the
automatic changeover press the
MODE key, until the LED AUTO (14)
is no longer illuminated.

Note:

Adjustments made to the heating
temperature and the service water
temperatures remain unchanged after
a power cut.

Adjustment of the heating
temperature and service water
temperature is undertaken using a
QAA73. (see page 23)

22 of 49

Commissioning

Preparation for operation

Display readout

Whilst the Boiler is in operation the
digital display (1) shows the flow
temperature of the Boiler whilst at the
same time LED (4) is illuminated.

By pressing SELECT button (7) the
following options are displayed in
succession:

LED (4) Flashing  Display

shows Hot Water Temperature
No readout (Display shows -.-)
LED (5) Lit Shows operational

Status of Boiler  

and (5) are off - Sequence

Status of the boiler shown as

follows:

0 Pause
1 No Heat Demand
2 Fan Ramp Up
3 Pre Purge
4 Changeover of Pre Purge to

ignition
5 Ignition
6 Flame Stabilisation / Rectification

10 Heating operation mode
11 Service water mode
20 Venting
22 Fan Run Down
99 Boiler Locked Out for

safety reasons

Locking code or information

relating to operating conditions of

heating appliance

Pressing Key (7) again will again
show the service water temperature
reading on the display. After a few
minutes the display returns to boiler
temperature.

Boiler Lock Out

If a malfunction occurs the Boiler will
Lock Out for safety reasons, the fault
is displayed by illumination of the LED
(3).
To restart the boiler: press RESET (6)
for approx 2 seconds. If the lock out
reoccurs, then check the gas supply to
the boiler, and/or the Flow / Return
Water isolation valves are open and
the boiler is above or below pressure
limitations.
If the lockout persists, contact MHS
Service department.

Use of flue cleaner key

The flue cleaner key (8) is only used
by a qualified specialist responsible
for maintenance, to undertake
calibration and carry out all checks
necessary for the correct operation of
the appliance. If the key is
inadvertently pressed, do not press
any other keys, but switch off the
appliance by means of adjusting knob
(10) and then switch on again.

23 of 49

Commissioning
Parameter adjustment on

control unit QAA73

Prerequisites for control unit QAA73
function

The EURON must be put into

"winter" mode viathe ‘Mode’
function key (see Page 21)

Legend

1 
2 
3 Minus Key Adjustment
4 Plus Key Adjustment
5 Service water standby Key
6 LCD Display
7 Heating circuit standby key
8 Parameter Code appears here
9 Rated temperature adjusting knob
10 Parameter value
11 Info Key
12 On/Off key

Application level

Key operation

Parameter range

QAA73 - User

Press program key 2  Scroll through Parameters

End User / Operator Parameter 1  50
(see Page 40)

QAA73 - Engineer

Press and Hold program keys 1 and 2 for approx 5
secs.

Specialist Parameter 51  98
(see page 41)

Back via "INFO" key

LMU

Key operation in this order:
Press and Hold Keys 4 and 1 for approx 5 secs.

Then for the next level (whilst in Parameters 516  727)
Keep program keys 1 and 2 pressed simultaneously for
approx a further 5 secs.

Engineer LMU Parameter 516  727
(See Page 42)

Specialist Engineer Parameter 501  755
(See Page 43 & 44)

In the corresponding parameter range

Parameters are selected using keys 1 and 2
Values are changed using keys 3 and 4

Press "INFO" key to return to normal operational / display mode

24 of 49

Commissioning

Flue gas quantities and adjustment

Flue gas measurement and
adjustment

Combustion settings need to be set
with the boiler in commissioning mode
(via Flue Cleaner button (8)), setting
the boiler at Maximum load / Minimum
load and making adjustments at the
gas valves Max Output and MinM
output as required. (Ref P24 & 25)
When in the commissioning mode the
3-way valve (Combi Only) is diverted
to heating mode, the temperature limit
values of the boiler are disabled and
only the maximum safety temperature
remains activated (Q5°C)

Whilst in commissioning mode to put
Boiler at max output turn Service
Water adjustment (11) fully clockwise,
to put boiler into minm output trun
service water adjustment (11) fully
anti-clockwise

If an HG model boiler (heating
operation only) is used with underfloor
heating, interrupt the operation of the
boiler if the temperature exceeds
45°C. Resume operation after the
boiler has cooled.

Access for Analyser Readings
First unscrew the locking screw (1)

between the flue gas test points.
The test point plugs (E= emission, A=

intake air) can be removed with a 90°
anti-clockwise turn (bayonet closure).

Place the analyser Sensor into the
appropriate Test point for measurment.
Flue gas measurement is carried out in
heat mode. Analyser sensor to go in
approx 75mm for Emission checking.

On a Combi If system load is difficult to
achieve, for example during the summer,
the hot water circuit can also be used as
follows:

With the aid of a screwdriver
disconnect the fixing clamps, 3, of
the motor, 4, of the 3-way valve.
Steady the motor with your hand
meanwhile detach the motor, open
one or more hot water taps to let off
the heat generated during the
measurement of the heating
appliance and carry out the
measurement.

When measuring is completed, shut the
taps again, attach the motor, push it
down and replace the fixing clamps.

25 of 49

Commissioning
Flue gas quantity and adjustment

Maximum output

Flue gas measuring and adjustment

Switch the boiler to commisioning mode,
while keeping flue cleaner key (8)
pressed, until the red LED (3) starts to
flash (double flash). The display shows
alternately the figures 1 and 00. With Hot
Water temperature Adjustment (11)
turned fully clockwise, the boiler is
working in heating mode at 100% output.
i.e. maximum output

Wait until the boiler stabilises and then
check the combustion settings, checking
for C02 value in conjunction with the chart
below.

To adjust the combusution, proceed as
follows:

Remove plastic cap and then
adjust High fire (1) on gas valve
using a flat bladed screw driver:
anticlockwise to increase and
clockwise to decrease the C02
value. Enusre correct settings for
corect fuel type is observed.

Note: Because of the sensitivity of
the adjustment, minimum
adjustments should only be made
Wait a few seconds, until the C0

2

value has stabilised, if applicable
repeat adjustment.

24 HG

30 HSG/HG

C02 [%]

C02 [%]

G20 Natural gas H

8,7-9,1

8,8 - 9,2

G31 Propane

10,7- 11,1

10,8 - 11,2

The measurement of C02 values must take place with appliance casing fitted.

26 of 49

Commissioning
Flue gas quantity and adjustment

Minimum output

Switch the boiler to commisioning
mode, while keeping flue cleaner key
(8) pressed, until the red LED (3)
starts to flash (double flash). The
display shows alternately the figures 1
and 00. With Hot Water Temperature
Adjustment (11) turned fully
clockwise, the boiler is working in
heating mode at 100% output. i.e.
maximum output

The boiler needs to be set for

operation at minimum load. Turn the
Hot water temperature adjustment
(11) anticlockwise as far as it will go
(the flow temperature of the boiler and
the figure 0 flash alternately on the
display). From this moment, the boiler
is working at minimum output.

Wait until the boiler stabilises and
then carry out the flue gas
measurement. Check the C02 value
at the same time by means of the
following chart.

24 HG

30 HSG/HG

C02 [%]

C02 [%]

G20 Natural gas H

9,3 -9,7

9,0 - 9,4

G31 Propane

10,9 - 11,3

10,8 - 11,2

The measurement of C02 values must take place with appliance casing fitted.

If values remain within the limits given
in the chart, no further regulation is
necessary.

After these measures the gas flow rate
on the counter should be checked,
taking into account the specifications
contained in the table of technical
data.

If the checks are completed, the
heating appliance must be re-set
manually to normal operation.
For this, keep the flue cleaner key
(8) pressed until the red LED (3)
goes out

If the measured values differ from the
values stated, proceed as follows:
(Numbers in the following text relate to
pictures above)

Remove the cap (2) using a

Torque T-40 bit then adjust the
Low Fire adjustment (3) on the gas
using the same T-40 bit: clockwise
to increase and anticlockwise to
decrease the C02 value of the
reading (because of the sensitivity
of the screw, minimum rotations
are sufficient)

Note: Because of the sensitivity of the
adjustment, minimum adjustments
should only be made, wait a few
seconds, until the C02 value has
stabilised, then if applicable repeat
adjustment.

After measuring, check again the
C02 values at High Fire. If High
fire requires any readjustment
also check and readjust Low Fire
as required.

3

27 of 49

Commissioning

Flue gas quantities and adjustment

Setting the Boiler for maximum heat
output (%)

The maximum heat output can be set
between the highest and lowest values
appropriate for the appliance or application.
The Boilers are preset in the factory at
100%.

The following steps can be followed to adjust
the output, set the appliance's operation at
the highest output

Press the Flue Cleaner Key (8), until the red
LED (3) starts to flash (double flash)

The display will now alternate between the
flow temperature of the boiler followed by the
figure 1 and then figure 00.

Using knob (11), service water temperature
adjustment, the maximum heat output, as a
percentage, can now be set to the required
value (see graph).

To store the adjustment, keep key (8)
pressed until the red LED (3) goes out.

Via the Parameter "d6" the the maximum
RPM of the fan for this setting in heating
operation can be shown (ref p29)

(Please note that this graph includes models not covered by this manual)

%

28 of 49

Commissioning

Safety check of heating appliance

Monitoring of the safety device
of the heating appliance

Checking the safety devices of the
boiler can be carried out using the
Flue Cleaner Key (8).

Press and hold the Flue Cleaner Key
(8) until the red LED (3) light is
illuminated then release immeadiatly.

Note: If the button is pressed for too
long i.e until the Red LED flashes with
a double flash then the boiler has
been put into Commissioning mode.
You will then need to reset and start
again.

Once in this mode the LED (3) will
flash and display will alternately flash
between "SF" and the boiler flow
temperature.

The boiler is now working at maximum
output in heating mode, and will
continue to do so until the safety
devices of the boiler are activated.
(On exceeding the temperature limit,
the appliance locks, the red LED (3)
flashes continually and the display
shows safety code 111.)

To resume operation, after cooling of
the appliance press RESET (6) key.

Protection system of heating
appliance

The boiler is protected from operating
faults by internal monitors in the
microprocessor circuit board, which
when necessary lock the appliance for
safety reasons. In the case of an
appliance being locked, a code is
shown on the display which gives the
type of locking and its cause. Two
types of locking can occur:

Safety Shut-Off

This type of fault is "temporary",
i.e. the fault is automatically
corrected, as soon as its cause is
corrected. Thereupon the
appliance switches itself on again
and resumes its normal operation.
While the appliance is in safety
stop, you can try to set it going
again by switching off and then on
again.
If safety switch-off occurs
repeatedly, please contact MHS
Service / Technical Support.

Locking

This type of fault is "Permanent",
the heating appliance can be reset
by pressing Key (6).

There follows a list with possible
operating messages and the
corresponding codes shown on the
display.

29 of 49

Commissioning

Parameters

Reading parameters only

Reading of the boiler parameters is
done by means of the SELECT (7)
key

 Keep the SELECT key (7)

pears on the

display (about 5 secs)

 release the key.
 Press the key again until "bO"

appears on the display (approx 5
secs.)

 Release the key.
 Now each time the key is

pressed, the display shows the
parameters shown on the right.

 When finished Keep the key

pressed tillfor approx 4 secs, until
the display shows "-.-."

 Release the key.
 The display now reverts to the

standard readout (heating flow
temperature).

Note: The display reverts to the
normal readout if no buttons are
pressed or adjustments made for
approx 8 minutes.

The only accessible reading
parameters are the following:

A0 Current fault readouts
A1 Boiler flow temperature reading

(°C)

A2 Service water temperature

reading(°C)
A3 not used
A4 Reading for operating phase of

boiler.
b0 Internal code in case of fault.
b1 Boiler return temperature reading

(°C)
b3 Reading of flue gas sensor

temperature
b4 Reading of outside temperature

(°C)
b5 not used
b6 not used
b7 Temperatuere of circuit of second

zone (°C)
b8 not used
b9 not used
C1 Reading for ionisation current (u.)
C2 Reading for ventilator revolutions

figure (thousands and hundreds)

C3 PWM fan (%)
C4 Reading of relative heating

appliance heat output (%)
C5 not used
C6 not used
C7 not used
d1 Setpoint, calculated according to

type of operation, service water

or heating operation.
d2 Value of calculated heating flow

temperatures (°C)
d3 Readout of set room temperature

value (°C) If no external/ambient

sensor is available, the value is

set at 20 °C
d4 Adjustment of value of service

water temperature (°C)
d5 not used
d6 Maximum fan speed in heating

operation (thousands and

hundreds)
d7 not used
d8 not used

30 of 49

Commissioning
Gas changeover

Changeover from natural gas to
liquid gas (LPG)

1. Disconnect the boiler from the
mains.

2. Shut the gas Isolation valve

3. Removing the boiler casing

4. Dismantle the mixing channel by
loosening the 3 screws (1).
Disconnect the electrical
Connections of the fan (3) and the
gas valve (4). Remove the air
intake hose (5).

5. Separate the gas valve from the
venturi by removing the 4 screws.

6. Install the gas injector (contained in
changeover kit), as shown in the
preceding illustrations.

7. Reinstall the ventilator/venturi
gauge/gas valve group in the
boiler.

8. Install the air screen (see chart
page 31) for liquid gas (contained
in changeover kit) on the left of the
heat exchanger.

The air screen is on the left of the heat
exchanger.

9. Connect the appliance to the
mains.

10. Open the gas isolation valve

11. Put the appliance into operation
according to the information in the
Instruction manual.

12. Check the gas seals.

13. Replace the front panel of the
combustion chamber.

14. Carry out a combustion analysis
and a calibration of the maximum
heat load.

15. Replace gas shield.

31 of 49

Commissioning
Gas changeover

Chart for gas changeover

Output

Gas type

Screen for gas

Screen for air

24 HG
G20/G25 Natural gas H/LL

None

None

G31 /Propane

0 4.6 mm

53/8mm

30 HSG/HG
G20/G25 Natural gas H/LL

None

None

G31 /Propane

0 4.6 mm

57/12,5mm

32 of 49

Chart for gas changeover

G20

Natural

Gas

H

G20/G25

Natural

Gas

H/LL

G25

Natural

Gas

LL

G30
Butane

G30/G31
Butane/
Propane

G31
Propane

o

I
CM

Lower Wobbe index
(15 °C, 1013 mbar) (MJ/m3)

45,67

37,38

80,58

70,69

Consumption
(15 °C, 1013 mbar)
(Natural gas = m3/h) (Liquid gas = kg/h)

max.

1,22

1,22

1,41

0,91

0,91

0,89

min.

0,32

0,32

0,37

0,24

0,24

0,23

Gas consumption after 10 Min.
(at 70% of max. output)
(Natural gas = m3/h) (Liquid gas = kg/h)

0,14

0,14

0,16

0,11

0,11

0,10

o

I
00

Lower Wobbe index
(15 °C, 1013 mbar) (MJ/m3)

45,67

37,38

80,58

70,69

Consumption
(15 °C, 1013 mbar)
(Natural gas = m3/h) (Liquid gas = kg/h)

max.

1,90

1,90

2,21

1,42

1,42

1,40

min.

0,49

0,49

0,57

0,36

0,36

0,36

Gas consumption after 10 Min.
(at 70% of max. output)
(Natural gas = m3/h) (Liquid gas = kg/h)

0,22

0,22

0,26

0,17

0,17

0,16

O

CO
I

—

o

I i­CM

Lower Wobbe index
(15 °C, 1013 mbar) (MJ/m3)

45,67

37,38

80,58

70,69

Consumption
(15 °C, 1013 mbar)
(Natural gas = m3/h) (Liquid gas = kg/h)

max.

2,43

2,43

2,83

1,81

1,81

1,79

min.

0,63

0,63

0,74

0,47

0,47

0,47

Gas consumption after 10 Min.
(at 70% of max. output)

0,28

0,28

0,33

0,21

0,21

0,21

O

CO
I

—

o

I o

CO

Lower Wobbe index
(15 °C, 1013 mbar) (MJ/m3)

45,7

45,7

37,38

80,58

80,58

70,69

Consumption
(15 °C, 1013 mbar)
(Natural gas = m3/h) (Liquid gas = kg/h)

max.

3,01

3,01

3,50

2,25

2,25

2,21

min.

0,75

0,75

0,87

0,56

0,56

0,55

Gas consumption after 10 Min.
(at70% of max. output
(Natural gas = m3/h) (Liquid gas = kg/h)

0,35

0,35

0,41

0,26

0,26

0,26

Commissioning

Gas changeover

33 of 49

Service and maintenance

Monitoring and checking

Maintenance is fundamentally
essential for the safe and correct
operation and long life of the boiler.
It is recommended, that
combustion analysis be carried out
at regular intervals, in order to
monitor the load and pollutant
emissions of the boiler.

If the boiler is decommissioned in an
area where the room temperature in
winter can fall below 0°C, it is advised
to mix the water of the boiler with
antifreeze, to avoid frequent
evacuation.
Check carefully when using antifreeze
if this is suitable for stainless steel,
from which the inner part of the
heating appliance is made.

The manufacturer is not liable for
damage to the appliance or the
equipment caused by use of
unsuitable antifreeze or additives

Before starting servicing

Before performing any servicing and
cleaning, the appliance must be
disconnected from the mains.
Gas supply isolator and Water
Isolation valves closed for both
heating and Hot water

34 of 49

Service and maintenance

Monitoring and checking

General remarks

At least once a year the appliance
should undergo the following
monitoring:

1. Check seals of water pipes and if
applicable replace.

2. Check seals of gas pipes and if
applicable replace as required.

3. Visual check of condition of all
boiler components.

4. Visual check of burner.

5. Cleaning of main heat exchanger

6. Check functional efficiency of
safety system:

i.e. Temperature protection.

7. Check functional efficiency of gas
feed safety system:

Gas and flame failure
protection (ionisation)

8. For Combi Boiler monitoring of
service water production efficiency
(checking through flow and
temperature).

9. Checking general functional
efficiency of boiler.

10. Remove any oxidization on the
electrode with the aid of an emery
cloth.

11. Check correct positioning / spark
gaps of the ignition and ionisation
electrodes as per the adjacent
picture.

12. Check the combustion fan blades
for debris build up. Remove any
debris with a soft bristle brush or
compressed air.

Cleaning of stainless steel heat
exchangers

For Cleaning the interior/dry side of the
heat exchanger coils, the burner / burner
door assembly must be removed.

For cleaning you may use water, a
cleaning agent (citric acid*) and use a
non-metal brush. Afterwards flush with
water.

Note: Never Clean the Burner itself
Cleaning of the Siphon

To gain access to the siphon, unscrew
the Condense collecting glass clockwise,
which is on the bottom left of the
underside of the boiler. Allow water to
drain out safely. Pour 2 litres of clean tap
water into the heat exchanger and allow
to drain safely through to the cleaning
point.

Refit the Condense Collecting Glass and
poor a further 2 litres of clean tap water
into the heat exchanger to ensure the
siphon is full of water.

If the appliance has not been used
for a long time, the siphon must be
filled before switching on again.

It is dangerous not to refill the siphon
with water, as in this case flue gas
can escape into the atmosphere.

Function checking

After completing the maintenance
work fill the heating circuit with a
pressure of around 1,0 bar and bleed
the appliance of air.
Also fill the service water appliance.

Set the appliance in operation. If
necessary, bleed the heating
appliance again. Check the
adjustments and correct operation
of all operator, calibration and
monitoring elements.

Check that the flue gas connection is
completely sealed with no cross
contamination to the combustion air
and is functioning correctly.

* Cleaning Granules availble from
MHS Spares Department

35 of 49

Locking

Display

Internal Code (bO)

Cause

91

EEPROM failure

92

Hardware failure of electronic circuit board

110

129

Activation of thermostats for underfloor heating

110

422

Locking because of over heating

113

506

Activation of flue gas sensor

133

102

Locking because of gas failure

151

Internal locking of circuit board

151

97

Flame at atart of reset phase

152

Failure in programming

153

259

Reset Button pressed when boiler not in fault

154

425

Flow temperature rising too rapidly or no circulation

160

83

On ignition necessary fan speed not achieved

160

282

Blocked Fan

161

110

Measured fan speed above upper limit

183

105

Circuit board in programming mode

Safety cut-off

Display

Internal Code (bO)

Cause

20

142

Short circuit in heating supply sensor

20

143

Heating supply sensor circuit open

40

144

Short circuit in heating return sensor

40

145

Heating return sensor circuit open

50

146

Short circuit in service water or water tank sensor

50

147

Service water or tank sensors circuit open

111

141

Flow temperature above temperature limit (90 °C)

119

140

Low Water Pressure

135

84

Quantity of fan revolutions not correct

154

401

Return temperature greater than flow temperature

154

433

At Supply and return too high

Service and Maintenance

Error Codes

36 of 49

Information code

Display

Internal Code (bO)

Cause

10

150

Short circuit in external/ambient sensor

10

151

External/ambient sensor circuit open

61

Remote control or room temperature sensor signal distrubed

62

Connection of an incompatible remote control or time switch

92

Failure of electronic hardware

133

101

Flame attend of safety period not detected

134

98

Extinguishing of flame during operation

180

168

Flue cleaner function active

Service and Maintenance

Error Codes

37 of 49

Maintenance and Service
Removing appliance cover

Bringing appliance into service position

Maintenance, Service and
cleaning must be carried out by
trained and approved Personnel.
This person shall be responsible
for correct implementation of
Mantainence activities.

See Page 11 for cover removal
details

Prior to maintenance work, the
appliance must be isolated from the
Electrical Mains Supply, Gas
Supply, and Water Flow and Return
connections shut off.

It is recommended that

Maintenance / Service works are
carried out once a year.
See P39

38 of 49

Maintenance and Service

Dismantling burner and heat exchanger

Dismantling Burner Door

 Remove all electrical connections
 Disconnect the screws (1) of the

mixing tube (2)

 Pull out ionisation electrode (4) and

ignition electrode (5) after loosening
fixing screws

 Loosen fixing screws (6) on burner
 Remove complete burner unit (7)

from heat exchanger

 Check surrounding seal (8) of

burner plate as well as the ceramic
fibre seal (9) for damage and
replace if necessary

Dismantling Heat exchanger

 Empty appliance of water
 Disconnect condensate drainage

hoses (10)

 Disconnect supply and return

connections (15)

 Remove both fixing clips (17)
 Loosen fixing screws (11) for heat

exchanger (12)

 Detach heat exchanger forwards
 Disconnect combustion chamber

insulation (13)

 Flush out heat exchanger (12) with

pure water (remove obstinate
impurities with fine synthetic brush
and flush out)

 Clean flue gas collection unit (14)

and check all seals (18)

 Reassemble all components in

reverse order.

39 of 49

Service and Maintenance

Maintenance, Service and
cleaning must be carried out by
trained and approved Personnel.
This person shall be responsible
for correct implementation of
Mantainence activities.

It is recommended that
Maintenance/Service works should be
carried out once a year. Cleaning of
the heat exchanger coils, as long
there is only minor contamination of
the coils, should be carried out at least
every 2 years.

 Measuring and recording of preset

emission values

 Switch off heating circuit breaker

and secure against coming on
again, or separate the appliance
on all poles from the mains

 Isolate the Gas Supply
 Dismantle appliance casing, bring

control panel into service position

 Dismantle compressor, gas valve

and burner unit

 Disconnect ignition cable. Check

ignition plugs for breaks, moisture
(damp/moist ignition plugs cause
malfunction messages - replace
ignition plugs)

 Visual check of burner (if

necessary clean with brush/nylon
brush or vacuum cleaner)

 Visual check of Fan and venturi

burner (if necessary clean with
brush/nylon brush or vacuum
cleaner)

 Disconnect combustion chamber

insulation

 Flush out heat exchanger with

pure water (remove obstinate
impurities with fine synthetic
brush and flush out)

 Clean siphon and refill with water

before assembly

 Check all connections of

condensate-carrying parts for
watertightness. Remove any
leaking condensate or other
dampness

 Check fixing screws, replace if

necessary.

 The dismantled seals for gas and

water carrying parts should be
replaced with new seals when
reassembling; this applies
especially for O rings on the gas
valve and all burner seals

 Reassemble appliance ready for

operation

 Open gas pipe and check for

watertightness

 Switch on heating circuit breaker
 Carry out function monitoring with

emissions measurement

 Values according to factory

specifications, readjust if
necessary

40 of 49

Service manual
Appendix

QAA 73 (End User Parameters)

Scroll through Parameters using key 2 (Up Button)  ref Page 22

Parameter

Number

Description

Options / Range

Recommended

Default

1

Current Time of Day.

00:00  24:00

Actual Time.

2

Current Date (Day / Month)

1 Jan  31 Dec

Actual Date.

3

Year

2000 - 2094

Actual Year.

5

Reduced Room Temperature Set Point.

Frost - Day

16ºC

6

Frost Protection Set Point (Room)

4 - Reduced

10ºC

7

HWS Target Temperature

20 - 60ºC

55ºC

10

Heating Zone - Day Selection

Mo  Su & Week

Day Required

11

Time Switch Heating Zone - First ON

00:00  24:00

06:00

12

Time Switch Heating Zone - First OFF

00:00  24:00

22:00

13

Time Switch Heating Zone - Second ON

00:00  24:00

--:--

14

Time Switch Heating Zone - Second OFF

00:00  24:00

--:--

15

Time Switch Heating Zone - Third ON

00:00  24:00

--:--

16

Time Switch Heating Zone - Third OFF

00:00  24:00

--:--

30

DHW Zone  Day Selection

Mo  Su & Week

Day Required

31

Time Switch Hot Water Zone - First ON

00:00  24:00

06:00

32

Time Switch Hot Water Zone - First OFF

00:00  24:00

22:00

33

Time Switch Hot Water Zone - Second ON

00:00  24:00

--:--

34

Time Switch Hot Water Zone - Second OFF

00:00  24:00

--:--

35

Time Switch Hot Water Zone - Third ON

00:00  24:00

--:--

36

Time Switch Hot Water Zone - Third OFF

00:00  24:00

--:--

40

Holiday Start Date

1 Jan  31 Dec

& Inactive

Inactive

41

Holiday End Date

1 Jan  31 Dec

& Inactive

Inactive

42

Room Temperature Operating Level During Holiday
Period.

Frost / Reduced

Frost

45

Default Reset of Time Switch Settings

YES / NO

NO

46

External Summer/Winter Changeover Temperature.



47

Display Language



English

50

Fault Code

0…..255

Review Only

41 of 49

Service manual
Appendix

QAA 73 (Engineer Parameters)

Press and Hold program keys 1 (Down button) and 2 (Up button) for approx 5 secs. Ref Page 22
* Lines are only displayed if the unit is operating in Open Therm Plus mode and if the boiler controller supports its function.

For Access to the LMU level: Access QAA73 Engineer Parameters as detailed above
For Access to LMU Parameters (i.e Line 100 upwards)

Press and Hold program keys 1 (Down button) and 2 (Up button) for approx 10 secs

Parameter

Number

Description

Options / Range

Recommended

Default

Service Values

51

Current Room Temperature Set Point (Heating Zone 1)



#

52*

Current Room Temperature Set Point (Heating Zone 2)



#

53*

Outside Air Temperature (Attenuated)

-

#

54*

Outside Air Temperature (Composite)

-

#

55*

Actual Value of HWS



#

56*

HWS Flow Rate



#

57*

Actual Boiler Return Temperature

-

#

58*

Actual Flue Gas Temperature

-

#

59*

Actual Solar Panel Temperature

-

#

61*

Actual solar Storage Tank Temperature

-

#

62

QAA73 Communication Mode (Open Therm Mode)

Lite / Plus

Plus

Heating Zone Temperature Set Points

70

Compensation Curves Set Point for Time Switch 1



32

71

Minimum Boiler Flow Temperature for Time Switch 1



8

72

Maximum Boiler Flow Temperature for Time Switch 1



80

73

Compensation Slope Parallel Displacement for Time
Switch 1

-

0.0

74*

Build Construction Type

Heavy / Light

Light

75*

Influence of Room Temperature on Boiler Operation

None / HC1

On HC1

76

Pump Switching Differential



0.5

77

Compensation Slope Auto Adaptation

Inactive/Active

Inactive

78

Optimum Start Time Maximum Shift Limitation (Minutes)



100

79

Optimum Stop Time Maximum Shift Limitation (Minutes)



30

80*

Compensation Curves Set Point for Time Switch 2



0 (32 if AGU

used)

81*

Minimum Boiler Flow Temperature for Time Switch 2



8

82*

Maximum Boiler Flow Temperature for Time Switch 2



8 (80 if AGU

used)

83*

Compensation Slope Parallel Displacement for Time
Switch 2

-

0.0

HWS Set Points

90*

Reduced HWS Set Point



40

91

HWS Enable Switching

TSP DHW..

TSP DHW

92*

Anti Legionella Function (Monday Morning 2,5 Hours Max)

On

On

93*

Operating mode for HWS (Eco setting)

With Eco / Without

Eco

Without Eco

General

95

Operational Lock

Off / On

Off

96*

Clock Operation

QAA73 / Boiler

QAA73

97

Summer Time Start



25 March

98

Summer Time End



25 Oct

42 of 49

Service manual
Appendix

LMU (Engineer Parameters)

To Access parameters 516  727 from QAA73
Press and Hold Keys 4 (+ Button) and 1(Down Button) for approx 5 secs. Ref page 22

Parameter

Name

Setting

Unit

Description

516

THG

25

ºC

Summer / Winter changeover temperature
(30 °C: Summer / Winter changeover disabled/not active)

520

dTrAbsenk

10

K

Drawdown of the room setpoint at timer connection
("dTrAbsenk" = 0: timer works directly off heating demand)

532

Sth1

15

Steepness of heat characteristic curve heating circuit 1

533

Sth2

8

Steepness of heat characteristic curve heating circuit 2

534

DtR1

0

K

Room setpoint adjustment heating circuit 1

535

DtR2

0

K

Room setpoint adjustment heating circuit 2

727

Diagnose

Code

43 of 49

Service manual
Appendix

LMU (Specialist Engineer Parameters)

For Access to the next level (whilst in Parameters 516  727)
Keep program keys 1 (Down Button) and 2 (Up Button) pressed simultaneously for approx a further 5 secs. Ref page 22

Parameter

Name

Setting

Unit

Description

504

TkSmax

85

ºC

Maximum boiler setpoint temperature (>= "TkSmin" and <= 90
°C) must be at least 3 K less than for "TkMax"

505

TkS standard

80

ºC

Boiler setpoint at standard outside air temperature

506

TvSmin

20

ºC

Minimum flow setpoint temperature (>= 20 °C and <=
"TvSmax")

507

TvSmax

80

ºC

Maximum flow setpoint temperature ( >= TvSmin and <= 90°C)

521

dTkTrNenn

20

K

Delta T Control: flow and return at standard Outside air
Temperature (>= 2,5 K and <= maximum "dTkTrMax")

522

dTkTrMax

25

K

Delta-T-control: maximum differential of the supply/return
temperature at standard Ouside Air temperature

537

NqmodNenn

30

Speed level of boiler pump in design point of heating installation
("NqmodNenn" <= "QmodDrehzStufen")

538

NqmodMin

40

%

Minimum pump speed permitted for the heating installation

541

PhzMax

100

%

Maximum modulation rate in heating mode (>= "LmodTL" and
<= "LmodVL")

551

Kon

2

Constant for rapid power fluctuation without ambient effect

552

Hydraulic

System

6

Hydraulic system adjustment

553

KonfigHks

553

Configuration of heating circuit (position YX, X for heating circuit
1, Y for heating circuit 2 of LMU...)[ Value: 0 no room unit effect,
1 heating circuit 1 of room unit, 2 heating circuit 2 of room unit]

555

KonfigRg1

0010000

Installation options for: DHW priority, installation frost
protection, modem function, {room thermostat input, timer
switch}; ({} not LMU7...)

558

KonfigRg4

1000000

Installation options for: DHW thermostat, water pressure
sensor, function changeover valve outlet {heat demand Q8,
construction} ({} not LMU7...)

561

KonfigRg7

0001000

installation options for: Pump modulation, Regulator delay

596

ZeitAufZu

135

s

Operating time of mixer engine (time off / time on)

605

LPBAdrGerNr

1

LPB unit number of the LMU...

606

LPBAdrSegNr

0

LPB segment number of the LMU...

610

LmodVL_QAA

100

%

Setpoint operation: Modulation air in normal load, upper limit
modulation area

614

KonfigEingang

1

Installation options (function) of programmable input of the
LMU...-Base

615

Konfigoutlet

0

Installation options (function) of relay outlet K2 of the LMU...­Base

618

KonfigEingangR

0

Installation options (function) of programmable input of relay
ClipIn

619

Konfigoutlet1R

0001010

Installation options function) of relay outlet 1 of the relay ClipIn

620

Konfigoutlet2R

0000001

Installation options (function) of relay outlet 2 of the relay ClipIn

For Access to the OEM level: Access Specialist Engineer Parameters as detailed above
Keep program keys 1 (Down Button) and 2 (Up Button) pressed simultaneously for approx 10 secs.
When asked for OEM code, Password = 1 (Down Button), 2 (Up Button), 4 (Plus Button), 3 (Minus Button), 4 (Plus Button)

44 of 49

Service manual
Appendix

LMU (Specialist Engineer Parameters) - continued

Parameter

Name

Setting

Unit

Description

621

Konfigoutlet3R

0000010

Installation options (function) of relay outlet 3 of the relay ClipIn

639

dTUeberhBegr

40

%

Limit of temperature super-elevation via the Delta Tcontrol (0
%: no elevation, 100 %: fully measured elevation)

646

LmodNull

0

%

Modulation air if automatic firing not in operation

656

KonfigRg10

0

Installation options for: burner block, drinking water DLH cycle
protection, DHW lag, blower/fan switch-off ({} not LMU7...)

657

TbwSollAleg

0

ºC

Setpoint of free-wheeling anti-legionella function (0 °C:
legionella function not active)

658

Estrichfunction

Rh1

0

Operating mode of the floor drying function for heating circuit 1

659

Estrichfunction

Rh2

0

Operating mode of the floor drying out function for heating
circuit 2

700

Stoer1

1st Historical Fault  Nº of Occurances

701

StrPn1

1st Historical Fault  Operating Phase

702

StrDia1

1st Historical Fault  Operating Error Code

703

Stoer2

2nd Historical Fault  Nº of Occurances

704

StrPn2

2nd Historical Fault  Operating Phase

705

StrDia2

2nd Historical Fault  Operating Error Code

706

Stoer3

3rd Historical Fault  Nº of Occurances

707

StrPn3

3rd Historical Fault  Operating Phase

708

StrDia3

3rd Historical Fault  Operating Error Code

709

Stoer4

4th Historical Fault  Nº of Occurances

710

StrPn4

4th Historical Fault  Operating Phase

711

StrDia4

4th Historical Fault  Operating Error Code

712

Stoer5

5th Historical Fault  Nº of Occurances

713

StrPn5

5th Historical Fault  Operating Phase

714

StrDia5

5th Historical Fault  Operating Error Code

715

Stör_akt

Current Historical fault  Nº of Occurances

716

StrPn_akt

Current Historical fault  Operating Phase

717

StrDia_akt

Current Historical fault  Operating Error Code

718

BetrStd

0

std

Burner operating time (total time burner On)

719

BetrStdHz

0

std

Operating time Heating mode

720

BetrStdBw

0

std

Operating time DHW mode

721

BetrStdZone

0

std

Zone operating time

722

InbetrSetz

0

Burner startup meter

724

MmiStatus

0000101

Operating mode adjustment: automatik, summer, winter

725

Sw Version

LMU

-

LMU Software version

728

StrAlba1

1st Historical Fault

729

StrAlba2

2nd Historical Fault

730

StrAlba3

3rd Historical Fault

731

StrAlba4

4th Historical Fault

732

StrAlba5

5th Historical Fault

733

StrAlba6

Current Historical Fault

755

IonStrom

Measured value of ionisation current

45 of 49

Service manual
Appendix

Flue Termination Guidelines

Please note that this diagram is only intended for reference purposes only and that definitie guidance should be sort from BS 5440­2:2000, BS6644:2005:2005 and/or IGE/UP/10 as appropriate.

46 of 49

Service manual
Appendix

Typical Hydraulic Schemes

Power for additional Heating Circulation Pump using AGU2.514 clip in module (Optional Extra)

Parameter Changes (Using QAA73)

552 = 51

558 = Bit 2  Set to 0 for HWS Sensor or 1 for HWS Volt free Enable (if used for Hot Water)

618 = 6

619 = 10

Note: QAA73 is required to enable required Parameter changes

For Hot Water Pump - Use Divertor valve connection in Boiler.
Cut off Connector and remake suitable connections for connection to HWS Pump wiring.

QAD36 Flow sensor wired to X51-01, terminals 1 & 2 on AGU2.514 clip in Module.

47 of 49

Service manual
Appendix

Typical Hydraulic Schemes

Parameters required for Euron Boilers In cascade using RVA47. OCI420 clip must be fitted for cascade LPB

communication.

RVA 47:

Para 16 = 30
Para 140 = 1
Para 141 = 0
Para 142 = 1

Euron 1: (Changes made using QAA73)
Para 516 = 30

Para 543 = 1
Para 552 = 80
Para 604 = Bit 4  Set to 1 (should already be at at 1) all others should be Zero
Para 605 = 2
Para 606 = 0

Euron 2: (Changes made using QAA73)
Para 516 = 30

Para 543 = 1
Para 552 = 80
Para 604 = Bit 4  Set to 1 (should already be at at 1) all others should be Zero
Para 605 = 3
Para 606 = 0

48 of 49

Notes

49 of 49

MHS

BOILER S

ELCO heating solutions.
Exclusively from MHS Boilers

3 Juniper West, Fenton Way
Southfields Business Park
Basildon, Essex SS15 6SJ Tel:
01268 546700 Fax: 01268
888250 www.mhsboilers.com

Manual Ref: L307