Baxi Maxflow Combi WM User guide

Baxi Maxflow Combi WM
Gas Fired Wall Mounted Combination Boiler
with Unvented Hot Water Storage
Installation and
Servicing Instructions
Please leave these instructions with the user
IMPORTANT: This boiler MUST be installed with
the Unvented Kit Part No. 247369 which is in
a separate box supplied with the boiler

2
Baxi UK Limited is one of the leading manufacturers of
domestic heating products in the UK.
Our first priority is to give a high quality service to our
customers. Quality is designed into every Baxi product
- products which fulfil the demands and needs of
customers, offering choice, efficiency and reliability.
To keep ahead of changing trends, we have made a
commitment to develop new ideas using the
latest technology - with the aim of continuing to make
the products that customers want to buy.
Everyone who works at Baxi has a commitment to
quality because we know that satisfied customers
mean continued success.
We hope you get a satisfactory service from Baxi. If
not, please let us know.
Baxi Maxflow Combi WM
G.C.No47 075 03
Baxi is a BS-EN ISO 9001
Accredited Company
The boiler meets the requirements of Statutory Instrument
“ The Boiler (Efficiency) Regulations 1993 No3083” and is
deemed to meet the requirements of Directive 92/42/EEC
on the energy efficiency requirements for new hot water
boilers fired with liquid or gaseous fuels:-
Type test for purpose of Regulation 5 certified by:
Notified Body 0051.
Product/Production certified by:
Notified Body 0051.
For GB/IE only.

3
1.0 Introduction 4
2.0 General Layout 5
3.0 Appliance Operation 6
4.0 Technical Data 7
5.0 Dimensions and Fixings 8
6.0 System Details 9
7.0 Site Requirements 13
8.0 Installation 18
9.0 Commissioning the Boiler 24
10.0 Servicing the Boiler 26
11.0 Changing Components 28
12.0 Illustrated Wiring Diagram 37
13.0 Fault Finding 38
14.0 Short Parts List 42
Section Page
Contents

Baxi UK Limited declare that no substances
harmful to health are contained in the appliance
or used during appliance manufacture.
1.1 Description
1. The Baxi Maxflow Combi WM is a fully automatic
gas fired wall mounted combination boiler
incorporating a 54 litre unvented hot water storage
cylinder. It is room sealed and fan assisted.
2. The boiler is designed for use with a fully
pumped, sealed and pressurised system and
provides central heating and hot water at mains
pressure. It incorporates a pump, diverter valve,
pressure relief valve, expansion vessel and
pressure gauge.
3. The boiler is set to provide a maximum output of
28.0 kW. This modulates in both Central Heating
and Domestic Hot Water modes depending on the
setting of the temperature controls, the water
temperature in the boiler and, in the case of
Domestic Hot Water mode, the temperature of the
stored water. See Section 3.1 for full details.
4. The boiler has been approved to the Building
Regulations for unvented hot water storage
systems and the Local Authority must be informed
of the intention to install.
IMPORTANT: The components supplied in
the box marked “Unvented Kit” MUST be
fitted to the mains water supply in
accordance with the instructions included.
The installation of unvented hot water storage
systems and their components must only be
carried out by suitably qualified personnel.
Consideration should be given to Building
Regulations document G3.
5. It is designed for use on Natural Gas (G20) and
can be converted to use Propane or Butane.
6. A label giving details of the model, serial number
and Gas Council number is situated on the rear of
the facia panel (Fig. 1).
7. The boiler data badge is positioned inside the
left hand outercase panel (Fig. 2).
8. The boiler is intended to be installed in
residential / commercial / light industrial E.M.C.
environments on a governed meter supply only.
9. The boiler must be installed with one of the
purpose designed flues such as the standard
horizontal flue kit.
10. All systems must be thoroughly flushed and
treated with inhibitor (see section 6.2).
1.2 Installation
1. The appliance is suitable for installation only in G.B.
and I.E. and should be installed in accordance with the
rules in force. For Ireland install in accordance with
I.S.813 “Installation of Gas Appliances”. The
installation must be carried out by a CORGI
Registered Installer or other competent person and be
in accordance with the relevant requirements of
current Gas Safety (Installation and Use) Regulations,
the Building Regulations (Scotland) (Consolidation),
the Local Building Regulations, the Current I.E.E.
Wiring Regulations and the bye laws of the Local
Water Undertaking. Where no specific instructions are
given, reference should be made to the relevant
BRITISH STANDARD CODES OF PRACTICE.
1.0 Introduction
4
“Benchmark”Log Book
As part of the industry-wide “Benchmark”initiative all Baxi boilers now
include an Installation, Commissioning and Service Record Log Book.
Please read the Log Book carefully and complete all sections relevant to
the appliance and installation. These include sections on the type of
controls employed, flushing the system, burner operating pressure etc.
The details of the Log Book will be required in the event of any warranty
work. Also, there is a section to be completed at each subsequent regular
service visit. The Log Book must be left with the user.
Fig. 1
Position of User Label
Facia Panel
Fig. 2
Data Badge
NOTE: This appliance must be installed in
accordance with the manufacturer’s instructions
and the regulations in force. Read the instructions
fully before installing or using the appliance.

2.0 General Layout
5
2.1 Layout
1. Fan Assembly
2. Sensing Electrode
3. Pressure Relief Valve
4. Automatic Air Vent
5. Circulation Pump
6. Gas Valve Assembly
7. Facia and Control Panel
8. Optional Integral Timer Position
9. Pressure Gauge
10. Electrical Box
11. Motorised Valve
12. Burner
13. Spark Electrode
14. Heat Exchanger
15. Expansion Vessel
16. Air Pressure Switch
17. Cylinder Safety Valve
18. Hot Water Storage Cylinder
19. Central Heating Temperature Control
20. Domestic Hot Water Temperature Control
21. ON/OFF Selector Switch
22. Indicator Neons
23. Reset Button
24. Flame Failure Reset Button
25. Pressure Gauge
2.2 Optional Extras
1. Various flue extensions, bends, vertical flue
kits, control accessories etc. are available as
optional extras. These are detailed in a separate
publication.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
16
15
17
18
RESET
21 2423 8
20 22 25
19
Fig. 3

3.0 Appliance Operation
6
3.1 Boiler Operation
1. The boiler operating mode is controlled by the
selector switch on the control panel. When set to
it will operate in the Domestic Hot Water and
Central Heating modes. For Domestic Hot Water only
the selector switch should be set to .
2. Domestic hot water supply always takes priority
over central heating. If a demand for hot water is
required during a central heating period, the boiler
will automatically switch to hot water mode until the
demand is satisfied i.e. storage water has reached
the set temperature. Interruption to the central
heating only occurs when there is a demand for hot
water and should not be apparent to the User.
3. Central Heating Mode (Fig. 4)
If there is a call for central heating the diverter valve
operates and the pump circulates the primary heating
water, operating the differential pressure switch. The
fan will run at full speed; once the air pressure switch
has been proved the burner will light. The burner
output then automatically adjusts to suit the system
demand; as the temperature of the heating water in
the boiler approaches that set by the adjustable
central heating control knob the burner output is
reduced. When this set temperature is reached, the
burner extinguishes and the fan stops. The pump
continues to run for 3 minutes to prevent residual
heat build up in the boiler. The burner will not relight
for 3 minutes unless there is a demand for domestic
hot water during this period.
4. Domestic Hot Water Mode (Fig. 5)
When there is a demand for hot water (temperature
of stored hot water is below that set by the
thermostat), the pump will start to circulate the
primary heating water, operating the differential
pressure switch. The fan will run at full speed; once
the air pressure switch has been proved the burner
will light. The burner output then automatically
adjusts to suit the demand required to raise the
temperature of the domestic hot water within the
store to the temperature set by the adjustable
domestic hot water control knob. When this
temperature is reached the burner extinguishes and
the fan stops. The pump continues to run for 3
minutes to prevent residual heat build up in the boiler.
When the hot water demand has been satisfied, the
3-way diverter valve operates to divert the primary
heating water to the central heating, if the selector is
set to and there is a C.H. demand.
IMPORTANT: When the selector switch is in the ‘0’
(OFF) position the electrical supply to the boiler is
isolated. The boiler will not operate and the integral
timer (if fitted) will require resetting once the selector
switch is turned to either the DHW or CH position
3.2 Frost Protection Mode
1. The frost protection feature will operate when the
selector switch is in the central heating and domestic
hot water mode.
The gas and electrical supplies to the boiler must be
on and the system pressure between 0.5 and 2.5 bar.
2. If the system temperature falls below 5°C, then
the boiler will fire until the water temperature has
been raised.
3. Further frost protection can be incorporated by
using a frost thermostat to protect the whole system.
3.3 Pump Protection
1. With the selector switch in either operating position
the pump will automatically operate for 1 minute in
every 24 hours to prevent sticking.
M
M
1
3
45
6
7
8
910
2
11
12
1314151617
18
19
20 21
22
23
24
25
1
3
45
6
7
8
910
2
11
12
1314151617
18
19
20 21
22
23
24
25
1 Main Heat Exchanger
2 Automatic Air Vent
3 Burner
4 Ignition Electrode
5 Flame Sensing Electrode
6 Differential Pressure Switch
7 Gas Valve
8 Primary Flow Temperature Sensor
9 3-Way Diverter Valve
10 Pump
11 By-Pass
12 Pressure Gauge
13 Gas Inlet
14 Heating Flow
15 Heating Return
16 Cold Water Inlet
17 Domestic Hot Water Outlet
18 Flow Restrictor
19 Hot Water Storage Temperature Sensor
20 Temperature/Pressure Relief Valve
21 Storage Cylinder
22 Secondary Heat Exchanger
23 Central Heating Expansion Vessel
24 Safety Limit Thermostat
25 Central Heating Pressure Relief Valve
26 Removable Filter in Return Manifold
Key
Central Heating Circuit
Domestic Hot Water Circuit
Fig. 4
Fig. 5
26
26

4.0 Technical Data
7
Flue Terminal Diameter 100mm
Dimensions Projection 93mm
Outercase Dimensions
Casing Height - 950mm
Overall Height Inc Flue - 1080mm
Casing Width - 600mm
Casing Depth - 450mm
Clearances
LH Side 20mm Min
RH Side 5mm Min
Above Casing 200mm Min
Below Casing 250mm Min
Front 450mm Min (For Servicing)
Front 5mm Min (In Operation)
Weights kg
Installation Lift Weight 70
Total Operational Weight 130
Pressures
CH Expansion Vessel bar
Nominal Pre-charge 0.8
Safety Discharge 3
Max Operating 2.5
Min Operating 0.5
Recommend Operating 1-2
Max Capacity of
CH System 125 litres
Primary Water Content
of Boiler 3.2 litres
Pressures bar
Max Operating 3.5
Min Operating 0.1
Min Operating Pressure
at 12 l/min 1.6
Flow Rates l/min
DHW Flow Rate
@ 30o C Rise 14
DHW Flow Rate
@ 35o C Rise 11.5
Min Working
DHW Flow Rate 1
Max. Flow Rate 16 l/min.
Built In Bypass l/h
Min Circulation Rate 200
(CH Primary Circuit)
e.g. TRVs all closed
Pump
Available Head See graph below
Connections copper tails
Gas Supply - 22mm
Central Heating Flow - 22mm
Central Heating Return - 22mm
Cold Water Mains Inlet - 15mm
DHW Flow - 15mm
Pressure Relief Discharge - 15mm
Recommended System
Temperature Drop 11°C20°F
Water Temperature
D.H.W. Flow Temp (adjustable)
5°C to 65°C max (± 5°C)
Water Storage Volume 54 litres
Water Temperature
C.H. Flow Temp (adjustable)
30°C to 82°C max (± 5°C)
Heat Input (gross) Max Min
C/H & DHW kW 31.1 11.9
Btu/h 106,130 40,610
Heat Output Max Min
kW 28.0 10.4
Btu/h 95,555 35,492
Electrical Supply 230V~ 50Hz
Power Consumption 190W
External Fuse Rating 3A
Internal Fuse Rating F2A
External Controls 230V switching
Electrical Protection IP44 (IPx4D)
(Appliance must be connected to an
earthed supply)
Appliance Category CAT II 2H 3+
Gas Rate
(Natural Gas) Max Min
(After 10 Mins) m3/h 3.29 1.26
ft3/h 116 44
Burner Pressure (Natural Gas)
Room sealed panel fitted
mbar 10.6 ± 0.5
in wg 4.24 ± 0.2
Inlet Pressure (Natural Gas)
mbar 20
in wg 8
Time To Raise Water Storage 50°C
13 minutes
DHW CircuitCentral Heating Primary Circuit
Reheat Time 70% of storage
10 minutes
Burner Injector (Natural Gas)
18 x 1.18mm Diameter
Appliance Type C12 C32
NoxClass 3
Unvented DHW Expansion Vessel
See Section 6.8 for information
This value is used in the UK Government’s
Standard Assessment Procedure (SAP) for
energy rating of dwellings. The test data from
which it has been calculated have been
certified by 0051.
SEDBUK Declaration For
Maxflow Combi WM
The seasonal efficiency (SEDBUK)
is 78.6 %
0
200 400 600 800
1
2
3
4
5
6
Metre wg
l/h
Pump - Available Head
0 1000 1200
LPG Gases / Propane and Butane
Burner Injector 18 x 0.69mm diameter
Burner Pressure
Propane mbar
in wg
Butane mbar
in wg
Inlet Pressures
mbar
in wg
Butane
28
11.2
Max Rate
35.5
14.2
27.5
11.0
Min Rate
7.6
3.0
4.1
1.6
Propane
37
14.8
DHW Store Temp./Pressure Relief Valve
Maximum Pressure 7 bar
Maximum Temperature 90°C
DHW Inlet Pressure Relief Valve
Maximum Pressure 6 bar

5.0 Dimensions and Fixings
8
DIMENSIONS
A950mm
B450mm
C600mm
D107mm ØMin.
E180mm
F160mm
G120mm
H160mm
360°Orientation in Steps of 45°
Tube Ø100mm
D
C
B
A
E
G
F
H
Hot Water
Outlet
(15mm)
Outer Case
Cold Mains
Inlet
(15mm)
Heating
Return
(22mm)
Heating
Flow
(22mm)
Safety
Valve
(15mm)
Gas
Inlet
(22mm)
62mm55mm55mm100mm100mm118mm 110mm

6.0 System Details
9
6.1 Information
1. The Baxi Maxflow Combi WM Combination
Boiler is a ‘Water Byelaws Scheme - Approved
Product’.
To comply with the Water Byelaws your attention is
drawn to the following installation requirements
and notes (IRN).
a) IRN 001 - See text of entry for
installation requirements
and notes.
b) IRN 302 - Byelaw 14.
2. Reference to the WRc publications, ‘Water
fittings and materials directory’and ‘Water supply
byelaws guide’give full details of byelaws and the
IRNs.
6.2 Central Heating Circuit
1. The appliance is suitable for fully pumped
SEALED SYSTEMS ONLY.
Treatment of Water Circulating Systems
•All recirculatory water systems will be subject to
corrosion unless an appropriate water treatment is
applied. This means that the efficiency of the
system will deteriorate as corrosion sludge
accumulates within the system, risking damage to
pump and valves, boiler noise and circulation
problems.
•For optimum performance after installation this
boiler and its associated central heating system
must be flushed in accordance with the guidelines
given in BS 7593 “Treatment of water in domestic
hot water central heating systems”.
•This must involve the use of a proprietary
cleanser, such as BetzDearborn Sentinel X300 or
X400, or Fernox Superfloc. Full instructions are
supplied with the products, but for immediate
information please contact BetzDearborn (0151
420 9563) or Fernox (01799 550 811) directly.
•For long term protection against corrosion and
scale, after flushing it is recommended that an
inhibitor such as BetzDearborn Sentinel X100, or
Fernox MB-1 or Copal is dosed in accordance with
the guidelines given in BS 7593.
Failure to flush and add inhibitor to the system
may invalidate the appliance warranty.
•It is important to check the inhibitor concentration
after installation, system modification and at every
service in accordance with the manufacturer’s
instructions. (Test kits are available from inhibitor
stockists.)
•For information or advice regarding any of the
above contact Baxi Technical Service.

6.0 System Details
10
6.3 Bypass
1. The boiler has an integral bypass and in most
cases this should suffice. However in certain
circumstances, e.g. on systems where there is a
high resistance and TRV’s are fitted to all the
radiators it may be necessary to fit an external
by-pass. For example, a 15mm pipe between the
flow and return controlled by a valve, or an
uncontrolled radiator.
6.4 System Control
1. The boiler is designed for use in a heating
system that incorporates external controls, i.e. a
minimum of a timer device.
2. Suitable timer kits are available as optional
extras.
3. For optimum operating conditions and
maximum economy the fitting of a programmable
thermostat, such as the Baxi Maxflow Combi WM
Controller, is recommended.

6.0 System Details
11
6.5 System Filling and Pressurising
1. A filling point connection on the central heating
return pipework must be provided to facilitate
initial filling and pressurising and also any
subsequent water loss replacement/refilling.
2. The filling method adopted must be in
accordance with all relevant water supply bye-
laws and use approved equipment.
3. Your attention is drawn to: IRN 302 and Byelaw
14.
4. The sealed primary circuits may be filled or
replenished by means of a temporary connection
between the circuit and a supply pipe, provided a
‘Listed’double check valve or some other no less
effective backflow prevention device is
permanently connected at the inlet to the circuit
and the temporary connection is removed after
use (Fig. 6).
6.6 Expansion Vessel (Fig. 7)
(Central Heating only)
1. The appliance expansion vessel is pre-charged
to 0.8 bar. Therefore, the cold fill pressure is 0.8
bar. The vessel is suitable for correct operation for
system capacities up to 125 litres (27.5gal). For
greater system capacities an additional expansion
vessel must be fitted - refer to BS 7074 Pt 1.
6.7 Pressure Relief Valve (Fig. 8)
1. The pressure relief valve is set at 3 bar,
therefore all pipework, fittings, etc. should be
suitable for pressures in excess of 3 bar.
2. The pressure relief discharge pipe should be
not less than 15mm dia, run continuously
downward, and discharge outside the building,
preferably over a drain. It should be routed in such
a manner that no hazard occurs to occupants or
causes damage to wiring or electrical
components. The end of the pipe should terminate
facing down and towards the wall (Fig. 9).
3. The discharge must not be above a window,
entrance or other public access. Consideration
must be given to the possibility that boiling
water/steam could discharge from the pipe.
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Stop Valve
Double
Check
Valve
DHW
Mains
Inlet
CH
Return
Temporary
Hose
Discharge Pipe
Pressure Relief Valve
Expansion Vessel

6.0 System Details
12
6.8 Domestic Hot Water Circuit
1. All DHW circuits, connections, fittings, etc.
should be fully in accordance with relevant
standards and water supply bye-laws.
2. Your attention is drawn to:
IRN 116 and the Water Supply (Water Fittings)
Regulations 1999 Schedule 2, Section 8,
paragraph 17. Sealed primary circuits and/or
secondary hot water systems shall incorporate a
means for accommodating the thermal expansion
of water to prevent any discharge from the circuit
and/or system, except in an emergency situation.
3. The boiler’s maximum working mains pressure
is 8 bar, therefore all pipework, connections,
fittings, etc. should be suitable for pressures in
excess of 8 bar. The pressure reducing valve
supplied in the ‘Unvented Kit’must be fitted. The
manufacturer of any outlet fittings, such as a
shower valve, may require a lower maximum
pressure. The pressure reduction must take
account of all fittings connected to the DHW
system.
6.9 Showers
1. If a shower control is supplied from the
appliance it should be of the thermostatic or
pressure balanced type. Thermostatic type
shower valves provide the best comfort and
guard against water at too high a temperature.
Existing controls may not be suitable - refer to the
shower valve manufacturer.
6.10 Hard Water Areas
1. If the area of the installation is recognised as a
HARD WATER AREA then a suitable device
should be fitted to treat the mains water supply to
the boiler.

7.0 Site Requirements
13
7.1 Information
1. The installation must be carried out by a CORGI
Registered Installer or other registered competent
person and be in accordance with the relevant
requirements of the current Gas Safety (Installation
and Use) Regulations, the Building Regulations
(Scotland)(Consolidation), the Local Building
Regulations, the current I.E.E. Wiring Regulations
and the bye laws of the Local Water Undertaking.
Where no specific instruction is given reference
should be made to the relevant British Standard
Codes of Practice. For Ireland install in accordance
with IS 813 “Installation of Gas Appliances”.
7.2 B.S. Codes of Practice
WARNING - The addition of anything that may
interfere with the normal operation of the
appliance without the express written permission
of Baxi UK Limited could invalidate the appliance
warranty and infringe the Gas Safety (Installation
and Use) Regulations.
7.3 Clearances (Fig. 11 & 12)
1. A flat vertical area is required for the installation
of the boiler.
2. The clearances around the outer case are for the
flue elbow, pipework etc. The clearance in front of
the appliance is for servicing purposes when
installed in a cupboard or compartment.
3. Additional clearances at the side must be left to
accommodate any rising pipework. It is not possible
to route any pipework within the outercase.
250mm Min
950mm
600mm
200mm Min
5mm Min
20mm Min
450mm Min
For Servicing
Purposes
5mm Min
In Operation
Fig. 11
Fig. 12
450mm
STANDARD
B.S. 6891
B.S. 5440: Pt 1
B.S. 5440: Pt 2
B.S. 5546
B.S. 7074
B.S. 5449: Pt 1
B.S. 6798
SCOPE
Gas Installation.
Flues.
Air Supply.
Installation of hot water supplies
for domestic purposes.
Expansion vessels and ancillary
equipment for sealed water systems.
Forced circulation hot water systems.
Installation of gas fired hot water
boilers.

7.0 Site Requirements
14
7.4 Location
1. The boiler may be fitted to any suitable wall with
the flue passing through an outside wall or roof
and discharging to atmosphere in a position
permitting satisfactory removal of combustion
products and providing an adequate air supply.
The wall must be capable of supporting the weight
of the appliance.
2. The boiler should be fitted within the building
unless otherwise protected by a suitable enclosure
i.e. garage or outhouse. (The boiler may be fitted
inside a cupboard - see Section 7.5).
3. If the boiler is sited in an unheated enclosure
then it is recommended to leave the ON/OFF
Selector Switch in the domestic hot water and
central heating position to give frost protection.
4. If the boiler is fitted in a room containing a bath
or shower reference must be made to the current
I.E.E. Wiring Regulations and Building
Regulations. If the boiler is to be fitted into a
building of timber frame construction then
reference must be made to the current edition of
Institute of Gas Engineers Publication IGE/UP/7
(Gas Installations in Timber Framed Housing).
7.5 Ventilation of Compartments
1. The boiler does not require any air vents in the
room in which it is installed. If it is installed in a
cupboard or compartment permanent air vents are
required at high and low levels (see Table 1). The
vents must communicate with the same room or
be direct to outside on the same wall.
2. When installed in a cupboard or compartment a
75mm clearance for air movement must be left in
front of the boiler when any door or panel is
closed.
7.6 Gas Supply
1. The gas installation should be in accordance
with BS6891.
2. The connection to the appliance is a 22mm
copper tail. This is connected to the gas service
cock (Fig. 14).
3. Ensure that the pipework from the meter to the
appliance is of adequate size. Do not use pipes of
a smaller diameter than the boiler gas connection
(22mm).
7.7 Electrical Supply
1. External wiring must be correctly earthed,
polarised and in accordance with current I.E.E.
Wiring Regulations.
2. The mains supply is 230V ~ 50Hz fused at 3A.
NOTE: The method of connection to the electricity
supply must facilitate complete electrical isolation
of the appliance.
Connection may be via a fused double-pole
isolator with a contact separation of at least 3mm
in all poles and servicing the boiler and system
controls only.
Free area of air vent (cm2)
Position of vent
High Level
Low Level
Air from room
310.5
310.5
Air from outside
155.25
155.25
Fig. 13
Fig. 14 Gas Service
Cock
Table 1

7.0 Site Requirements
15
7.8 Flue
1. The following guidelines indicate the general
requirements for siting balanced flue terminals.
Recommendations for flues are given in BS 5440
Pt.1.
2. If the terminal discharges onto a pathway or
passageway, check that combustion products will
not cause a nuisance and that the terminal will
not obstruct the passageway.
3. If a terminal is less than 2 metres above a
balcony, above ground or above a flat roof to
which people have access, then a suitable
terminal guard must be provided.
Terminal Position with Minimum Distance (Fig. 16) (mm)
A Directly below an openable window, air vent or any other
ventilation opening. 300
B Below gutter, drain/soil pipe. 150
C Below eaves. 200
D Below a balcony/car port roof. 200
E From vertical drain pipes and soil pipes. 150
F From internal or external corners. 300
G Above adjacent ground or balcony level. 300
H From a surface facing a terminal. 600
I Facing a terminal. 1200
J From opening (door/window) in carport into dwelling. 1200
K Vertically from a terminal on the same wall. 1500
L Horizontally from a terminal on the same wall. 300
M Above an opening, air brick, opening window etc. 300
N Horizontally to an opening, air brick, opening window etc. 300
Vertical Flues - minimum distance to edge of terminal mm
P Above the roof level (to base of terminal). 300
Q From adjacent wall to flue. 300
R From adjacent opening window. 1000
S From another terminal. 600
Fig. 16
Q
R
P
S
L
G
G
E
J
D
K
G
AAD
F
H,I
B,C
F
Likely flue positions requiring
a flue terminal guard
M
N

7.0 Site Requirements
16
7.9 Flue Dimensions
The standard horizontal flue kit allows for flue
lengths between 100mm and 1m from elbow to
terminal (Fig. 17).
The maximum permissible equivalent flue
length is: 4 metres.
NOTE: Each additional 45°of flue bend will
account for an equivalent flue length of 0.5m.
eg. 45°= 0.5m, 90°= 2 x 45°= 1m etc.
7.10 Flue Terminal Trim
1. Once the flue is secure the trim can be fitted if
required.
2. Remove the protective backing from the
adhesive seal. Apply the seal to the rear of the
trim flange (Fig. 18).
3. Locate the trim over the flue terminal and push
it back to the wall to compress the seal (Fig. 19).
7.11 Terminal Guard (Fig. 20)
1. When codes of practice dictate the use of
terminal guards, they can be obtained from most
Plumbers’and Builders’Merchants.
2. There must be a clearance of at least 50mm
between any part of the terminal and the guard.
3. When ordering a terminal guard, quote the
appliance name and model number.
4. The flue terminal guard should be positioned
centrally over the terminal and fixed as illustrated.
Fig. 17
Fig. 20
100mm 1m
Fig. 19
Fig. 18
Flue Trim
Adhesive Seal

17
7.0 Site Requirements
7.12 Flue Options
1. The Baxi Maxflow Combi WM can be fitted with
flue systems as illustrated.
2. The standard flue is suitable only for horizontal
applications.
3. Maximum permissible equivalent flue lengths
are:-
Horizontal 4.0 metres
Vertical 4.0 metres
Vertical (Twin Pipe) 15.0 metres
4. Any additional “in line”bends in the flue system
must be taken into consideration.
Their equivalent lengths are:-
Concentric Pipes:
45°bend 0.5 metres
90°bend 1.0 metres
Twin Flue Pipe
45°bend 0.25 metres
90°bend 0.50 metres
The elbow supplied with the standard horizontal
flue is not included in any equivalent length
calculations. This elbow is of the same type as
the optional concentric 90°bend.
Bends can be used to route the flue pipe around
obstacles within the dwelling and to enable the
flue terminal to be positioned according to
requirements.
By combining two 45°bends and a straight piece,
a wide 90°bend can be achieved.
As it is possible to rotate the bends through 360°,
various “S”bends can be produced.
5. The illustrations opposite show examples of
maximum equivalent lengths.
6. Full details of part numbers and descriptions of
all optional flue components and kits can be
found in the Baxi Gas Central Heating Boilers
Installers’Guide.
7. Instructions for guidance and fitting are
included in each kit where appropriate.
Horizontal
Flues
Vertical
Flues
Vertical
Flues
(Twin Pipe)
Maximum Length = 3m inc. 2 x 45°bends
Maximum Length = 14m
inc. 4 x 45°bends
Maximum Length = 2m
inc. 2 x 90°bends

8.0 Installation
18
8.1 Initial Preparation & Fitting the Boiler
The gas supply, gas type and pressure must be
checked for suitability before connection (see
Section 7.6).
1. Locate the wall template (Fig. 21) in the
appliance packaging.
2. After considering the site requirements
(see Section 7.0) position the template on the wall
ensuring it is level both horizontally and vertically.
3. Select the six most suitable fixing holes and
mark their position.
4. Mark the centre of the flue hole (rear exit). For
side exit, mark as shown. If required, mark the
position of the gas and water pipes. Remove the
template.
5. Cut the hole for the flue (minimum diameter
107mm).
6. Drill and plug the mounting bracket fixing holes.
7. Using the screws and washers provided, secure
the mounting bracket to the wall.
8. Lift the boiler and locate the slots in the upper
chassis over the hooks on the mounting bracket
(Fig. 22).
THIS OPERATION WILL REQUIRE
ASSISTANCE !
9. Remove the sealing plugs from the gas and
water connections.
10. Connect the gas and water valves together with
the appropriate copper tail ensuring that the sealing
washers are correctly fitted.
NOTE: The rubber gas sealing washers are an
integral part of the gas valve.
8.2 Flushing
1. Thoroughly flush the system - see Section 6.2.
Maxflow Combi WM
FIXING TEMPLATE
Gas Inlet
Safety Valve
Mounting Hooks
Mounting Bracket
Mounting Slots
Heating Flow
Heating Return
Cold Water Inlet
Hot Water Outlet
General Area For
Electrical Supply
Appliance Outline
107mm Dia Minimum
Aperture For Flue Tube
Mounting Bracket
160mm
For Side Flue Exit
Fig. 21
Fig. 22

8.0 Installation
19
8.3 Fitting the Pressure Relief
Discharge Pipe (Fig. 24)
1. Remove the discharge pipe from the kit.
2. Determine the routing of the discharge pipe in
the vicinity of the boiler. Make up as much of the
pipework as is practical, including the discharge
pipe supplied.
3. The pipework must be at least 15mm diameter
and run continuously downwards to a discharge
point outside the building. See section 6.7 for
further details.
4. Utilising one of the sealing washers, connect
the discharge pipe to the adaptor and tighten the
nut.
5. Complete the discharge pipework and route it
to the outside discharge point.
8.4 Unvented Hot Water Storage
NOTE: The installation is subject to Building
Regulations approval and the Local Authority
must be informed of the intent to install.
Consideration must be given to Building
Regulations document G3.
1. The components supplied in the box marked
“Unvented Kit”MUST be fitted to the mains water
supply.
2. No isolating valves must be fitted between
these components and the boiler.
3. The combined filter and pressure reducing
valve must ideally be fitted before the mains
water supply divides to feed the boiler and the
rest of the dwelling.
4. The discharge pipes from the expansion relief
valve supplied in the kit and the
temperature/pressure relief valve on the boiler
storage cylinder must be routed to the tundish
supplied.
5. These discharge pipes must be 15mm, and the
pipe downstream of the tundish at least 22mm.
6. See Section 8.5 and the instructions supplied
in the unvented kit for full details.
Fig. 23
Fig. 24
Pressure Relief Valve
Adaptor
Discharge Pipe

8.0 Installation
20
8.5 Unvented Hot Water Store Discharge
Pipe
1. The discharge pipe from the tundish should
terminate in a safe place where there is no risk to
persons in the vicinity of the discharge, be of metal
and:-
•Be at least one pipe size larger than the nominal
outlet size of the safety device unless its total
equivalent hydraulic resistance exceeds that of a
straight pipe 9m long i.e. discharge pipes between
9m and 18m equivalent resistance length should be
at least 2 sizes larger than the nominal outlet size
of the safety device, between 18m and 27m at least
3 sizes larger, and so on. Bends must be taken into
account in calculating the flow resistance. See
Table 2.
•Have a vertical section of pipe at least 300mm
long below the tundish before any elbows or bends
in the pipework.
•Be installed with a continuous fall.
•Have discharges visible at both the tundish and
the final point of discharge but where this is not
possible or practically difficult there should be clear
visibility at one or other of these locations.
Examples of acceptable discharge arrangements
are:
i) Ideally below a fixed grating and above the water
seal in a trapped gully.
ii) Downward discharges at a low level, i.e. up to
100mm above external surfaces such as car parks,
hard standings, grassed areas etc. are acceptable
providing that where children may play or otherwise
come into contact with discharges, a wire cage or
similar guard is positioned to prevent contact, whilst
still maintaining visibility.
iii) Discharges at high level, e.g. in to metal hopper
and metal down pipe with the end of the discharge
pipe clearly visible (tundish visible or not) or onto a
roof capable of withstanding high temperature
discharges of water and 3m from any plastic
guttering systems that would collect such
discharges (tundish visible).
iv) Where a single pipe serves a number of
discharges, such as in blocks of flats, the number
served should be limited to not more than 6
systems so that any installation can be traced
reasonably easily. The single common discharge
pipe should be at least one pipe size larger than the
largest individual discharge pipe to be connected. If
unvented hot water storage systems are installed
where discharges from safety devices may not be
apparent, i.e. in dwellings occupied by blind, infirm
or disabled people, consideration should be given
to the installation of an electronically operated
device to warn when discharge takes place.
Note: The discharge will consist of scalding water
and steam. Asphalt, roofing felt and non-metallic
rainwater goods may be damaged by such
discharges.
12. See Figs. 24a and 24b for typical discharge
pipe terminations.
G 1/2
G 3/4
G1
15mm
22mm
28mm
22mm
28mm
35mm
28mm
35mm
42mm
35mm
42mm
54mm
up to 9m
up to 18m
up to 27m
up to 9m
up to 18m
up to 27m
up to 9m
up to 18m
up to 27m
0.8m
1.0m
1.4m
1.0m
1.4m
1.7m
1.4m
1.7m
2.3m
Valve
outlet
size
Minimum
size of
discharge
pipe D1
Minimum
size of
discharge
pipe D2 from
tundish
Maximum resistance
allowed, expressed
as a length of
straight pipe (i.e. no
elbows or bends)
Resistance
created by
each elbow
or bend
Table 2
Worked Example of Discharge Pipe Length
Calculation
•The example is for a G 1/2 temperature relief
valve with a discharge pipe (D2) having 4 elbows
and an actual length of 7.0m from the tundish to
the point of discharge.
From Table 2:-
•The maximum equivalent resistance of a length
of 22mm discharge pipe (D2) from a G 1/2
temperature relief valve is 9.0m.
•The equivalent resistance of 4 x 22mm elbows
at 0.8m each is 3.2m. Subtract this from the total
permissible equivalent length
i.e. 9.0m - 3.2m = 5.8m
•Therefore the maximum permissible actual
length of 22mm pipe when including 4 elbows is
5.8m. As this is less than the actual length
required (7.0m) a calculation must be performed
for the next largest size.
•The maximum equivalent resistance of a length
of 28mm discharge pipe (D2) from a G 1/2
temperature relief valve is 18.0m.
•The equivalent resistance of 4 x 28mm elbows
at 1.0m per bend is 4.0m. Subtract this from the
total permissible equivalent length
i.e. 18.0m - 4.0m = 14.0m.
•As the actual length is 7.0m a 28mm discharge
pipe (D2) will be adequate.
Tundish
500mm
max.
300mm
min.
Safety Device
(e.g. temperature relief valve)
Low Level Discharge Pipe Termination
Discharge below
fixed grating
Metal discharge pipe D1 from
temperature relief valve to tundish
Metal discharge pipe D2 from
tundish with continuous fall
Fixed
grating
Trapped
gulley
Termination into a hopper Termination into a gulley
Alternative Discharge Pipe Terminations
Wall Termination
Fig. 24a
Fig. 24b