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

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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.

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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
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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.