Baxi Maxflow Combi FS User guide

Baxi Maxflow Combi FS
Gas Fired Floor Standing 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 FS
G.C.No47 075 10
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 40
13.0 Fault Finding 41
14.0 Short Parts List 45
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 FS is a fully automatic
gas fired floor standing 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 domestic 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. The
controls are behind the facia cover panel (Fig. 1).
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 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. The components supplied in the box marked
“Unvented Kit”MUST be fitted to the mains water
supply in accordance with the instructions included.
6. It is designed for use on Natural Gas (G20) and
can be converted to use Propane or Butane.
7. A label giving details of the model, serial number
and Gas Council number is situated on the wiring
cover panel (Fig. 2).
8. The boiler data badge is positioned on the boiler
base panel (Fig. 2).
9. The boiler is intended to be installed in
residential / commercial / light industrial E.M.C.
environments on a governed meter supply only.
10. The boiler must be installed with one of the
purpose designed flues such as the standard
horizontal flue kit.
11. 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
Fig. 2
Data Badge
User Label
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.
Facia Panel
Facia Cover
Panel

2.0 General Layout
5
2.1 Layout
1. Central Heating Flow
2. Pressure Relief Valve
3. Central Heating Return
4. Domestic Hot Water Flow
5. Mains Water Inlet
6. Gas Inlet
7. Domestic Hot Water Storage Cylinder
8. Storage Cylinder Heating Coil
9. Expansion Vessel
10. Domestic Hot Water Storage Drain
11. Heating Coil Drain
12. Circulation Pump
13. Gas Valve
14. Burner
15. Heat Exchanger
16. Fan/Hood assembly
17. Air Pressure Switch
18. Electrical Cover Panel
19. Temperature Gauge
20. Position For Optional Integral Timer
21. Facia Cover Panel
22. Facia
23. Overheat Thermostat
24. Flow Temperature Sensor
25. Electrical Control Box
26. Temperature Gauge Sensor
27. Filling Loop Connections
28. Diverter Valve
29. Storage Cylinder Temperature Sensor
30. Indicator Neons
31. Domestic Hot Water Temperature Control
32. ON/OFF Selector Switch
33. Central Heating Temperature Control
34. Flame Failure Reset Button
35. Reset Button
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.
Fig. 3
1
2
345
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24 25 26 27 28 29
33
32
31
34
35
30
1
2
3
4
Unvented Kit - Principal
Components
1. Pressure Reducing Valve
2. Expansion Relief Valve
3. Tundish
4. DHW Expansion Vessel

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
13456
7
89
10
2
11
12
13
14
15 16
17
18 19 20
21
22 23
24
M
1 Heating Flow
2 Central Heating Pressure Relief Valve
3 Heating Return
4 Domestic Hot Water Outlet
5 Cold Water Inlet
6 Gas Inlet
7 By-Pass
8 Safety Limit Thermostat
9 Primary Flow Temperature Sensor
10 3-Way Diverter Valve
11 Hot Water Storage Temperature Sensor
12 Main Heat Exchanger
13 Temperature/Pressure Relief Valve
14 Central Heating Expansion Vessel
15 Ignition Electrode
16 Burner
17 Differential Pressure Switch
18 Flame Sensing Electrode
19 Automatic Air Vent
20 Gas Valve
21 Pressure Gauge
22 Pump
23 Storage Cylinder Heating Coil
24 Storage Cylinder
Key
Central Heating Circuit
Domestic Hot Water Circuit
Fig. 4
Fig. 5
13456
7
89
10
2
11
12
13
14
15 16
17
18 19 20
21
22 23
24

4.0 Technical Data
7
Flue Terminal Diameter 100mm
Dimensions Projection 93mm
Outercase Dimensions
Casing Height - 850mm
Casing Width - 600mm
Casing Depth - 630mm
Clearances
LH Side 5mm Min
RH Side 5mm Min
Above Casing 500mm Min
Front 500mm Min (For Servicing)
Front 5mm Min (In Operation)
Weights kg
Packaged Weight (gross) 95
Installation Lift Weight 83
Total Operational Weight 140
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 l/30min
DHW Flow Rate
Continuous@ 30o C Rise 14
DHW Flow Rate
Continuous @ 35o C Rise 11.4
Storage Flow Rate
@ 30o C Rise 450
Min Working
DHW Flow Rate 1
Max. Flow Rate 18 l/min.
Built In Bypass l/h
Min Circulation Rate 215
(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
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 40610
Heat Output Max Min
C/H & DHW 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 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
Max Min
mbar 11.8 ± 0.5 1.8 ± 0.2
in wg 4.7 ± 0.2 0.72 ± 0.2
Inlet Pressure (Natural Gas)
mbar 20
in wg 8
Time To Raise Water Storage 50°C
9 minutes
DHW CircuitCentral Heating Primary Circuit
Reheat Time 70% of storage
8 minutes
Burner Injector (Natural Gas)
18 x 1.18mm Diameter
Appliance Type C12 C32
NOxClass 3
Unvented DHW Expansion Vessel
See Sections 6.8 & 8.6 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 FS
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
28.2
11.3
Min Rate
7.6
3.0
4.0
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
A630mm
B850mm
C107mm ØMin.
D600mm
E100mm ØMin.
F93mm
G120mm
A
G
C
C
F
E
B
D
Outer Case
Rear of Case
View From Above
Centre line of pressure relief valve is
803mm above floor level.
All others are 823mm above floor level.
50mm
Gas
Inlet
(22mm)
Cold
Mains
Inlet
(15mm)
Hot
Water
Outlet
(15mm)
Heating
Return
(22mm)
Pressure Relief
Valve
(22mm)
Heating
Flow
(22mm)
80mm 60mm 50mm 40mm 40mm

6.0 System Details
9
6.1 Information
1. The Baxi Maxflow Combi FS 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 the Baxi Helpline.

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
Combi 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. There are connection points on the mains cold
water inlet and central heating return isolating
taps to which the optional filling loop kit (Part No.
248221) can be assembled.
3. The filling method adopted must be in
accordance with the Water Supply (Water Fittings)
regulations and the Water Bylaws (Scotland).
4. Your attention is drawn to: Paragraph 24 of
Schedule 2 Section 8 of the publication Water
Regulations Guide which gives recommendations
and guidance on approved methods for filling
sealed systems.
5. The sealed primary circuits may be filled or
replenished by means of a temporary connection
between the primary circuit and a supply pipe
provided the arrangement in accordance with
Diagram R24.2a of the Water Regulations Guide.
6. The temporary hose must be completely
removed at both ends after use.
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
Stop
Valve

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, the Water Supply (Water Fittings)
Regulations and the Water Bylaws (Scotland).
2. Your attention is drawn to:
Schedule 2, Section 6 of the publication Water
Regulations Guide which relates to backflow
prevention.
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. The boiler should be positioned 120mm from the
wall to allow for access to pipework and fitting of
the isolating valves.
2. Sufficient clearance must be left at one side to
accommodate the components of the unvented kit.
The clearance should be at least 300mm to fit the
D.H.W. expansion vessel, tundish and attendant
pipework.
IMPORTANT: When installing a left hand flue
system it is not practical to site the components
of the unvented kit to the left of the boiler.
3. The floor must be flat and level extending for
720mm out from the wall and 600mm wide.
4. The minimum clear spaces needed around the
boiler measured from the casing are as follows:
Top - 10mm (In operation)
- 500mm (For servicing)
Any panel/work top above the unit must be easily
removable for servicing and other maintenance.
Left hand side - 5mm
Right hand side - 5mm
Front - 500mm (For Servicing)
35mm (In operation)
Rear - 120mm
Fig. 11
Fig. 12
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.
4020 8060 °C
850mm
600mm
5mm
500mm
10mm
Removable Section of Work Top
120mm
600mm
500mm
For Servicing
35mm
In Operation

7.0 Site Requirements
14
7.4 Location
1. The boiler must be positioned on a flat and level
floor or base which must be capable of supporting
the full operational weight of the boiler. The flue
must pass through an outside wall or roof and
discharge to atmosphere in a position permitting
satisfactory removal of combustion products and
providing an adequate air supply.
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
the minimum clearances must be maintained.
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
Table 1
Gas Cock

7.0 Site Requirements
15
7.8 Flue
1. The flue terminal position must always be
in accordance with the current edition of B.S.
5440 Part 1, and either Part J of the Building
Regulations England and Wales or Part J of
the Building Standards (Scotland)
Regulations as appropriate.
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. 10) (mm)
A Directly below an openable window, air vent or any other
ventilation opening. 300
B Below gutters, drain or soil pipes. 25
C Below eaves. 25
D Below balconies or car port roof. 25
E From vertical drain pipes and soil pipes. 25
F From internal or external corners. 25
G Above ground or balcony level. 300
H From a surface facing a terminal. 600
I Facing a terminal. 1200
J For an opening (door/window) in car port 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
Fig. 10
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
300 min
Terminal
Assembly
Top View Rear Flue
Property Boundary Line

7.0 Site Requirements
16
7.9 Flue Dimensions
When routed to the rear the flue must be at least
295mm long, plus the thickness of the wall. The
maximum length when using the standard flue kit
is 1m from adaptor to terminal .
The maximum permissible equivalent flue
length is: 5 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 model number.
4. The flue terminal guard should be positioned
centrally over the terminal and fixed as illustrated.
Fig. 17
Fig. 20
1m
Fig. 19
Fig. 18
Flue Trim
Adhesive Seal

17
7.0 Site Requirements
7.12 Flue Options
1. The Baxi Maxflow Combi FS 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 5.0 metres
Vertical 3.0 metres
Vertical (Twin Pipe) 10.0 metres
4. Any “in line”bends in the flue system must be
taken into consideration, including where a 90°
bend is connected directly to the boiler when the
flue is taken vertically or to the left.
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
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.
7.13 Extensions & Additional Elbows
1. The method of connecting any flue extensions
or additional elbows is the same as that for
connecting the standard flue and 90°elbow as
described in Section 8.3.
2. If, for example, when a flue extension is
connected to a 90°elbow the flue duct will project
from the air duct at the unconnected end by the
same amount as the flue duct spigot does from
the elbow . Further elbows or extensions can then
be added to this.
3. Similarly, a concentric flue can be connected to
the boiler adaptor in the same manner as it does
to the elbow to provide a vertical flue.
4. The additional 90°elbow available is identical
to the elbow supplied with the standard flue. 45°
elbows are of the same principle.
5. Extensions can be cut according to the
requirements of the installation.
Horizontal
Flues
Vertical
Flues
Vertical
Flues
(Twin Pipe)
Maximum Length = 3m
inc. 2 x 90°bends
Maximum Length Measurements to be
taken from Flue Adaptor - view from rear
Maximum Length = 8m
inc. 4 x 90°bends
Maximum Length = 1m
inc. 2 x 90°bends
Maximum Length = 2m
inc. 2 x 45°bends

460
8.0 Installation
18
8.1 Initial Preparation
The gas supply, gas type and pressure must be
checked for suitability before connection (see
Section 7.6).
1. Mark the centre of the flue hole as shown (Figs.
21 & 22). If required, mark the position of the gas
and water pipes (see Section 5.0).
2. Cut the hole for the flue (minimum diameter
107mm).
3. Ensure that the floor or base on to which the
boiler is to be fitted is clean and free from debris.
4. Install all pipework that will be behind the boiler,
including the pressure relief discharge pipe (see
section 6.7) and components and pipework of the
domestic hot water Unvented Kit.
8.2 Flushing
1. Connect a tube to the central heating flow or
return pipe.
2. Flush thoroughly (see Section 6.2 of System
Details).
3. The Baxi Combi filling loop kit can be used to
flush the system.
IMPORTANT: Do not use any safety valves to
flush or drain the system.
A
B
560
95
205
560
560
Left Hand
Side Flue
X= Dimension dependent
upon individual installation
circumstances
Rear Flue
65
X
View From Rear
A= Concentric Adaptor/
Twin Flue Duct
B= Twin Flue
Air Duct
Profile of Outercase
Top
Fig. 21
Fig. 22

Wall Thickness
8.0 Installation
19
8.3 Rear Flue
To route the flue to the rear it is necessary to use
the horizontal flue kit (Part No. 247719). This kit
includes a 90°bend, clips and seals, clamp, and a
flue trim. Any other extensions or bends can also
be purchased as required.
When the flue is routed directly out to the rear the
bend and one clip and seal are not required.
1. Measure the wall thickness (Fig. 23). To this
dimension add 295mm.
2. The sum of this shall be known as dimension “X”.
3. Mark dimension “X”on the air duct, measuring
from the joint of the duct and terminal. The
remainder is waste material (Fig. 24).
4. Measure the length of waste and transfer the
dimension to the flue duct (Fig. 24).
5. Remove the waste from both ducts. Ensure that
the cut ends are square and free from burrs.
6. Take the rubber seal and position it on the boiler
adaptor. Using the flue duct clamp secure the flue
duct to the adaptor (Fig. 25).
7. Slide the clip over the cut end of the air duct.
Engage the air duct over the flue duct, ensuring
that the flue duct fully engages in the flue terminal
(Fig. 26).
8. Position the rubber seal equally over the joint
between the air duct and adaptor. Align the clip
with the seal and tighten the screws (Fig. 27).
9. Manoeuvre the boiler backwards into position,
keeping as straight as possible to avoid damaging
the flue as it passes through the wall. Connect the
system pipe work as described in Section 8.5
8.4 Left Side and Vertical Flue
To route the flue to either the left hand side or
vertically it is necessary to use a 0.25m flue
extension kit (Part No. 248189). A horizontal flue kit
(Part No. 247719) or 90°flue elbow kit (Part No.
247725) and vertical flue terminal kit (Part No.
246140) will also be required.
Any other extensions or bends can also be
purchased as required.
1. Mark a dimension of 130mm on both the flue
and air duct of the 0.25m extension and cut.
Discard the remainder. Ensure that the cut ends
are square and free from burrs.
2. Take the rubber seal and position it on the boiler
adaptor (Fig. 28). Using the flue duct clamp secure
the flue duct to the adaptor (Fig. 29). (cont.)
IMPORTANT : Fitting the Flue
•The complete flue system must be fitted to the appliance before positioning when the
wall against which the boiler is being installed is that through which the flue will
terminate.
•When routing either to the left or vertically, sufficient length of flue must be fitted to the
boiler to ensure that it extends outside the outercase. This will enable connection of the
remainder of the flue system once the boiler is in position.
•A rear flue that will pass through one or more walls before the outside wall should be
long enough to protrude through the first wall when the boiler is in position. This will
enable connection of the remainder of the flue system.
Waste
(X)
Waste
Fig. 24
Fig. 23
Fig. 25
Fig. 26
Fig. 27
Air Duct
Flue Duct
Rubber Seal
Flue Duct Clamp
Flue Duct
Air Duct
Clip
Flue Adaptor
Sample Point

8.0 Installation
20
8.4 Left Side and Vertical Flue (cont)
3. Slide the clip over one end of the air duct.
Engage the air duct over the flue duct.
4. Position the rubber seal equally over the joint
between the air duct and adaptor. Align the clip
with the seal and tighten the screws.
5. To fit the elbow take the rubber seal and
position it on the air duct. Pass the clip over the
air duct.
6. Engage the flue elbow on the air and flue ducts
and pull the seal to equally cover the joint.
7. Set the elbow to the required orientation. Align
the clip over the seal and tighten the screws
(Fig. 30).
8. Manoeuvre the boiler backwards into position,
and proceed to fit any extensions or bends as
required and the appropriate terminal.
8.5 Connecting the Pipework (Fig. 31)
1. Connect the three brass extension pieces to
the CH flow, CH return and gas inlet adaptors on
the tap rail. Connect the fixed nuts to the
adaptors.
2. Connect two of the isolating cocks to the CH
flow and CH return extension pieces. Ensure that
the flow arrow on each tap is correctly oriented
and visible.
3. Loosely fit two of the 22mm copper elbows to
the CH flow and CH return taps and connect
them to the system pipework. Complete the
soldered joints.
4. Loosely fit the 15mm copper elbows to the
DHW flow and cold water inlet adaptors and
connect them to the system pipework. Complete
the soldered joints.
5. Connect the remaining isolating cock to the
gas supply extension piece and loosely fit the
remaining 22mm copper elbow to the gas supply
pipe. Complete the soldered joint.
6. Connect the copper extension piece to the
pressure relief adaptor on the tap rail. Ensure that
a 15mm fibre washer is between the joint.
7. Take the length of 15mm copper discharge
pipe from the kit and connect it to the pressure
relief valve. Fit the valve to the copper extension
and discharge pipe using fibre washers.
8. Disconnect all pipes and insert the correct
washer between the joints - fibre for water and
rubber for gas.
9. Tighten all pipe joints and ensure that the
square tap on each isolating cock will not prevent
correct fitting of the case top panel.
Fig. 28
Fig. 29
Rubber Seal
90°Elbow
Flue Adaptor
Clip
Rubber Seal
Flue Duct Clamp
Flue Duct
Air Duct
Flue Adaptor
Central Heating Flow
Extension Piece
Pressure Relief Valve
Central Heating Return
Domestic Hot Water Flow
Mains Water Inlet
Gas Inlet
Fig. 30
Fig. 31