Keston Combi C35 User manual

EVERYTHING IS POSSIBLE
Combi C30 & C35
USER GUIDE
July 2018 UIN 215417 A04
When replacing any part on this appliance, use only spare parts that you can be assured
conform to the safety and performance specification that we require. Do not use
reconditioned or copy parts that have not been clearly authorised by Keston.
For the very latest copy of literature for specification and maintenance practices visit our
website www.keston.co.uk where you can download the relevant information in PDF
format.

2
THE BENCHMARK SERVICE INTERVAL RECORD MUST BE COMPLETED AFTER EACH SERVICE
Keston is a member of the Benchmark scheme and fully supports the aims of the programme.
Benchmark has been introduced to improve the standards of installation and commissioning of central
heating systems in the UK and to encourage the regular servicing of all central heating systems to
ensure safety and efciency.
CONTENTS
1. Introduction ................................................... 3
Safety .............................................................. 3
Electricity Supply ............................................. 3
Important Notes............................................... 3
2. Boiler Operation ............................................ 4
Controls Diagram............................................. 4
To Start the Boiler ............................................ 4
Operation Modes............................................. 5
Preheat Domestic Hot Water........................... 5
Control of Water Temperature ......................... 5
Efcient Heating System Operation................. 6
Weather Compensation................................... 6
Boiler Frost Protection..................................... 6
Boiler Restart................................................... 6
Mains Power Off.............................................. 6
3. System Water Pressure ................................ 7
4. Condensate Drain.......................................... 8
5. General Information ...................................... 9
Boiler Pump..................................................... 9
Minimum Clearances....................................... 9
Escape of Gas................................................. 9
Cleaning .......................................................... 9
Maintenance.................................................... 9
6. Points for the Boiler User ........................... 10
Troubleshooting..............................................11
7. Display Functions -
Normal Operation .. 12-13
8. Display Functions - Settings Changed...... 13
9. Display Functions - Fault Messages..... 14-18
All Gas Safe Register installers carry a Gas Safe Register ID card, and have a registration number. Both should be recorded in the
Benchmark Commissioning Checklist. You can check your installer by calling Gas Safe Register direct on 0800 4085500.

3
1. INTRODUCTION
The Keston Combi C is a combination boiler providing both
central heating and instantaneous domestic hot water. Featuring
full sequence automatic ignition and fan assisted combustion.
Due to the high efciency of the boiler, condensate is produced
from the ue gases and this is drained to a suitable disposal point
through a plastic waste pipe at the base of the boiler. A condensate
‘plume’ will also be visible at the ue terminal.
Safety
CURRENT GAS SAFETY (INSTALLATION & USE)
REGULATIONS OR RULES IN FORCE.
In your own interest, and that of safety, it is the law that this
boiler must be installed by a Gas Safe Registered Engineer, in
accordance with the above regulations.
In IE, the installation must be carried out by a Registered Gas Installer
(RGII) and installed in accordance with the current edition of I.S. 813
“Domestic Gas Installations”, the current Building Regulations and
reference should be made to the current ETCI rules for electrical
installation.
It is essential that the instructions in this booklet are strictly
followed, for safe and economical operation of the boiler.
ELECTRICITY SUPPLY
This appliance must be earthed.
Supply: 230 V ~ 50 Hz. The fusing should be 3A.
IMPORTANT NOTES
• This appliance must not be operated without the casing
correctly tted and forming an adequate seal.
• If the boiler is installed in a compartment then the
compartment MUST NOT be used for storage purposes.
•
If it is known or suspected that a fault exists on the boiler
then it MUST NOT BE USED until the fault has been
corrected by a Gas Safe Registered Engineer or in IE a
Registered Gas Installer (RGII).
•Under NO circumstances should any of the sealed
components on this appliance be used incorrectly or
tampered with.
• This appliance can be used by children
8 years and above. Also persons with
reduced physical, sensory or mental
capabilities, or lack of experience
and knowledge, provided they have
been given supervision or instruction
concerning use of the appliance in a
safe way and understand the hazards
involved. Children shall not play with
the appliance. Cleaning and user
maintenance shall not be made by
children without supervision.

4
MINMAX MIN
MODECENTRAL HEATINGHOT WATER
e
BOILER
OFF
MAX
Legend
A. Domestic Hot Water Preheat On/Off Knob
B. Domestic Hot Water Temperature Knob
C. Central Heating Temperature Knob
D. Mode Knob
E. Boiler Status
F. Burner ‘on’ Indicator
G. System Pressure Gauge
H. Central Heating Economy Setting
TO START THE BOILER
If a programmer is tted refer to separate instructions for the
programmer before continuing.
Start the boiler as follows:
1. Set the mode knob (C) to ‘BOILER OFF’.
2. Set the Domestic Hot Water temperature knob (A) and
Central Heating temperature knob (B) to ‘MAX’.
3. Ensure that all hot water taps are turned off.
5.
Switch on electricity to the boiler and check that all external
controls, e.g. programmer and room thermostat, are on.
4. Set the mode knob (C) to ‘ ’ (winter).
The boiler will commence ignition sequence, supplying heat to
the central heating, if required.
Note. In normal operation the boiler status display (D) will display
messages (see section 7).
Note. Boiler frost protection - boiler will re if temperature is below 5ºC.
During normal operation the burner on symbol (E) will remain
illuminated when the burner is lit.
Note. If the boiler fails to light after ve attempts the following
fault messages will be displayed:
To restart the boiler, press restart. The boiler will repeat the ignition
sequence. If the boiler still fails to light consult a Registered Gas
Installer, or in IE a Registered Gas Installer (RGII).
2. BOILER OPERATION
Legend
A.
Domestic Hot Water Temperature Knob
B. Central Heating Temperature Knob
C. Mode Knob
D. Boiler Status Display
E. Burner ‘on’ Indicator
F. Central Heating Economy Setting
G. Pressure Gauge
H. Restart Button
I. Preheat button
AG DI HE B F C
Ignition Lockout 1/2
Check Other Gas
Appliances Work
Restart Boiler
Restart Menu
Ignition Lockout 2/2
If Fault Persists
Contact Installer
Restart Menu

5
OPERATION MODES
Winter Conditions -
(Central Heating and Domestic Hot Water
required)
Set the mode knob (C) ‘ ’ (winter).
The boiler will re and supply heat to the radiators.
The domestic hot water preheat will operate with the preheat
button (I) set to ‘Preheat On’.
Summer Conditions - (Domestic Hot Water only required)
Set the mode knob (C) to ‘ ’ (summer).
Set the central heating demand on the external controls to OFF.
The domestic hot water preheat will operate with the preheat
knob (I) set to ‘Hot Water On’.
Boiler Off
Set the mode knob (C) to ‘BOILER OFF’. The boiler mains
power supply must be left on to enable frost protection (see
Frost Protection).
PREHEAT - DOMESTIC HOT WATER
The domestic hot water heat exchanger within the boiler can
be kept preheated to provide faster delivery of hot water at the
tap. This is achieved by pressing the “PREHEAT” button to
‘PREHEAT ON’.
The boiler will operate periodically for a few seconds to
maintain the domestic hot water heat exchanger in a preheated
condition. The average time period between operation is 90
minutes. This may vary considerably due to the surrounding
ambient temperature of the boiler. The boiler will operate
whenever there is a demand for domestic hot water.
If standard hot water delivery is satisfactory press the
“PREHEAT” button to ‘PREHEAT OFF’.
CONTROL OF WATER TEMPERATURE
Domestic Hot Water
The domestic hot water temperature is limited by the boiler
controls to a maximum temperature of 65ºC, adjustable via
the domestic hot water temperature knob (A). However at
low DHW draw off rates the maximum temperature may
exceed 65ºC.
Approximate temperatures for domestic hot water:
Knob Setting Hot Water Temperature (approx.)
Minimum 40ºC
Maximum 65ºC
Due to system variations and seasonal temperature
uctuations domestic hot water ow rates/temperature rise
will vary, requiring adjustment at the tap : the lower the ow
rate the higher the temperature, and vice versa.
Central Heating
The boiler controls the central heating radiator temperature
to a maximum of 80
o
C, adjustable via the central heating
temperature knob (B).
Approximate temperatures for central heating:
Knob Setting Central Heating Radiator Temperature (approx.)
Minimum 30ºC
Maximum 80ºC
For economy setting ‘ ’ refer to Efcient Heating System
Operation.

6
EFFICIENT HEATING SYSTEM OPERATION
The boiler is a high efciency, condensing appliance which
will automatically adjust its output to match the demand for
heat. Therefore gas consumption is reduced as the heat
demand is reduced.
The boiler condenses water from the ue gases when operating
most efciently. To operate your boiler efciently (using less
gas) turn the central heating temperature knob (B) to the ‘
‘ position or lower. In winter periods it may be necessary
to turn the knob towards the ‘max’ position to meet heating
requirements. This will depend on the house and radiators
used.
Reducing the room thermostat setting by 1ºC can reduce gas
consumption by up to 10%.
WEATHER COMPENSATION
When the Weather Compensation Kit (supplied as standard) is
tted to the system then the central heating temperature knob
(B) becomes a method of controlling room temperature. Turn
the knob clockwise to increase room temperature and anti-
clockwise to decrease room temperature. Once the desired
setting has been achieved, leave the knob in this position
and the system will automatically achieve the desired room
temperature for all outside weather conditions.
BOILER FROST PROTECTION
The boiler is tted with frost protection that operates in all
modes, provided the power supply to the boiler is always
turned on. If the water in the boiler falls below 5ºC, the frost
protection will activate and run the boiler to avoid freezing.
The process does not guarantee that all other parts of the
system will be protected.
If a system frost thermostat has been installed, the boiler
must be set in winter mode, ‘ ’, for the system frost
protection to run.
If no system frost protection is provided and frost is likely
during a short absence from home it is recommended to leave
the system heating controls or built in programmer (if tted)
switched on and run at a reduced temperature setting. For
longer periods, the entire system should be drained.
BOILER RESTART
To restart the boiler, when directed in the listed fault messages
(see section 9), press “Restart”. The boiler will repeat its
ignition sequence. If the boiler still fails to start consult a
Gas Safe Registered Engineer or in IE a Registered Gas
Installer (RGII).
MAINS POWER OFF
To remove all power to the boiler the mains power switch
must be turned off.

7
3. SYSTEM WATER PRESSURE
The system pressure gauge (G - see page 4) indicates the central heating system pressure.
If the pressure is seen to fall below the original installation pressure of 1-2 bar over a period
of time and continue to fall then a water leak may be indicated. In this event re-pressurise the
system as shown below. If unable to do so or if the pressure continues to drop a Gas Safe
Registered Engineer or in IE a Registered Gas Installer (RGII) should be consulted.
THE BOILER WILL NOT OPERATE IF THE PRESSURE HAS REDUCED TO LESS THAN 0.3 BAR UNDER THIS CONDITION.
Cap
Plug
Filling Loop
B
A
Filling Position
Starting Position
Cap
Filling Loop
Handle
(Blue)
Domestic Hot Water
(DHW) Inlet Valve
Filling
Loop
B
A
Plug
To Top up the system :-
1. Ensure both A& Bhandles (blue) are in closed position
(as shown below)
2. Remove the plug and cap and retain.
3.
Connect the lling loop to the Domestic Hot Water (DHW) inlet
and tighten. Also ensure that the other end of lling loop is
hand tight.
4. Turn the Domestic Hot Water (DHW) Inlet Ablue handle
to the horizontal position.
5. Ensuring no leaks are seen, gradually turn the lling loop
handle (blue) Bto the horizontal position.
6. Wait for the pressure gauge to reach 1 to 1.5 bar.
7. Once pressure is reached turn valves A& Bback to
the closed position.
8. Disconnect the lling loop, replace cap and plug. Note
there can be some water spillage at this point.

8
4. CONDENSATE DRAIN
This appliance is tted with a siphonic condensate trap system
that reduces the risk of the appliance condensate from freezing.
However should the condensate pipe to this appliance freeze,
please follow these instructions:
a. If you do not feel competent to carry out the defrosting
instructions below please call your local Gas Safe
Registered installer for assistance.
b.
If you do feel competent to carry out the following instructions
please do so with care when handling hot utensils. Do not
attempt to thaw pipework above ground level.
If this appliance develops a blockage in its condensate pipe, its
condensate will build up to a point where it will make a gurgling
noise prior to locking out displaying “Ignition Lockout” on the
display. If the appliance is restarted it will make a gurgling noise
prior to it locking out displaying “Ignition Lockout” on the display..
To unblock a frozen condensate pipe;
1. Follow the routing of the plastic pipe from its exit point on
the appliance, through its route to its termination point.
Locate the frozen blockage. It is likely that the pipe is
frozen at the most exposed point external to the building
or where there is some obstruction to ow. This could be
at the open end of the pipe, at a bend or elbow, or where
there is a dip in the pipe in which condensate can collect.
The location of the blockage should be identied as closely
as possible before taking further action.
2. Apply a hot water bottle, microwaveable heat pack or a
warm damp cloth to the frozen blockage area. Several
applications may have to be made before it fully defrosts.
Warm water can also be poured onto the pipe from a
watering can or similar. DO NOT use boiling water.
3. Caution when using warm water as this may freeze and
cause other localised hazards.
4.
Once the blockage is removed and the condensate can ow
freely, restart the appliance. (Refer to “To Start the boiler”)
5. If the appliance fails to ignite, call your Gas Safe Registered
engineer.
Preventative Solutions
During cold weather, set the central heating temperature knob
(B) to maximum, (Must return to original setting once cold
spell is over).
Place the heating on continuous and turn the room thermostat
down to 15ºC overnight or when unoccupied. (Return to normal
after cold spell).

9
5. GENERAL INFORMATION
BOILER PUMP
The boiler pump will operate briey as a self-check once every
24 hours, regardless of system demand.
MINIMUM CLEARANCES
Clearance of 165mm (6 1/2”) above, 100mm (4”) below, 2.5mm
(91/8”) at the sides and 450mm (17 3/4”) at the front of the boiler
casing must be allowed for servicing.
BOTTOM CLEARANCE
Bottom clearance after installation can be reduced to 5mm
This must be obtained with an easily removable panel, to enable
the system pressure gauge to be visible and to provide the
100mm clearance required for servicing.
SERVICE REQUEST FUNCTION
When the boiler has been installed for more than 1 year the following
message will appear on screen:
Press “Restart” to clear this message.
ESCAPE OF GAS
Should a gas leak or fault be suspected contact the National Gas
Emergency Service without delay. Telephone [phone].
Ensure that;
- All naked ames are extinguished
- Do not operate electrical switches
- Open all windows and doors
CLEANING
For normal cleaning simply dust with a dry cloth. To remove stubborn
marks and stains, wipe with a damp cloth and nish off with a dry
cloth. DO NOT use abrasive cleaning materials.
MAINTENANCE
The appliance should be serviced at least once a year by a Gas
Safe Registered Engineer or in IE a Registered Gas Installer
(RGII).

10
6. POINTS FOR THE BOILER USER
Note. In line with our current warranty policy we would ask that you check through the following guide to identify any
problems external to the boiler prior to requesting a service engineers visit. Should the problem be found to be other
than with the appliance we reserve the right to levy a charge for the visit, or for any pre-arranged visit where access is
not gained by the engineer.
FOR ANY QUERIES PLEASE RING THE
KESTON CONSUMER HELPLINE : 01482 443005
NOTE. BOILER RESTART PROCEDURE -
To restart boiler, press the Restart button.

11
YES
NO HOT WATER
Check the mains power is turned
on and ensure mode knob (C) is
in the summer or winter position
Is water coming out of the hot
water tap when turned on?
NO CENTRAL HEATING
Check the mains power is turned
on and ensure mode knob (C) is
in the winter position
Does the boiler operate and
provide central heating?
Check the time settings on the
programmer are as you require
and adjust if necessary
Check the programmer (internal
or external to the boiler) is in
an “ON” position and the room
thermostat is turned up
NO HOT WATER OR
CENTRAL HEATING
Check the mains power is turned
on and ensure mode knob (C) is
in the winter position
See boiler “Display Functions”
section
Does the boiler have a display
showing on the front control
panel?
See boiler “Display Functions”
section. If “Boiler off” is displayed
then contact Keston Customer
Services Helpline if your
appliance is under warranty or a
Gas Safe Registered Engineer,
in IE a Registered Gas Installer
(RGII), if out of warranty
YES
NO
Contact a Gas Safe Registered
Engineer or in IE a Registered
Gas Installer (RGII)
TROUBLESHOOTING
Contact a Gas Safe Registered
Engineer or in IE a Registered Gas
Installer (RGII)
See boiler “Display Functions”
section. If “Boiler off” is displayed
then contact a Gas Safe
Registered Engineer or in IE a
Registered Gas Installer (RGII)
NO
YES
NO

12
7. DISPLAY FUNCTIONS - NORMAL OPERATION MODE
Note. The temperatures shown below are for illustration purposes only. The measured temperatures will be shown on the boiler.
Mode Knob in “BOILER OFF”
position:
Domestic hot water operation
with call for CH:
Mode knob in “ ” position and
no heat demand:
Central Heating Operaton:
Mode knob in “ ” and no
heat demand:
Preheat operation:
Domestic hot water operation
without call for CH:
Boiler frost protection:

13
8. DISPLAY FUNCTIONS - SETTINGS CHANGED
Note. The temperatures shown below are for illustration purposes only. The measured temperatures will be shown on the boiler.
DHW temperature knob
moved:
Pre-Heat
If preheat is switched on, then the boiler will periodically re the
burner. Thereby reducing the time taken to provide hot water.
If preheat is switched off the response time will be reduced,
although gas consumption will also be reduced.
Service required:
CH temperature knob
moved:
CH temperature knob
moved with outside sensor
connected:
To switch preheat off press
the “Hot Water Preheat On”
button:
To switch preheat on press
the “Hot Water Preheat Off”
button:

14
9. DISPLAY FUNCTIONS - FAULT MESSAGES
Outside Sensor Fault
Contact Installer
Restart Menu
PCB Fault
Contact Installer
Restart Menu
Too Many Restarts
Contact Installer
Restart Menu
Low Mains Voltage
Contact Electricity Provider
Menu
BOILER DISPLAY MESSAGE ACTION
Restart the appliance - if the boiler fails to operate then please contact Keston (if under
warranty) or alternatively a Gas Safe Registered Engineer if outside of the warranty period.
In IE contact a Registered Gas Installer (RGII).
Contact a qualied electrician or your electricty provider.
Uncongured PCB. Please contact Keston (if under warranty) or alternatively a Gas Safe
Registered Engineer if outside of the warranty period. In IE contact a Registered Gas
Installer (RGII).
1. Turn power off and on at the fused spur.
2. If the boiler fails to operate plese contact Keston (if under wrranty) or alternatively a
Gas Safe Registered Engineer if outside of the warranty period. In IE contact a Registered
Gas Installer (RGII).

15
9. (CONT’D) DISPLAY FUNCTIONS - FAULT MESSAGES
Flame on Before Gas On
Contact Installer
Restart Menu
BOILER DISPLAY MESSAGE ACTION
Restart the appliance - if the boiler fails to operate then please contact Keston (if under
warranty) or alternatively a Gas Safe Registered Engineer if outside of the warranty period.
In IE contact a Registered Gas Installer (RGII).
Check system pressure is between 1 & 1.5bar on the pressure gauge. If the boiler fails to
operate then plese contact Keston (if under warranty) or alternatively a Gas Safe Registered
Engineer if outside of the warranty period. In IE contact a Registered Gas Installer (RGII).
Water Pressure 1/3
With Boiler Off &
System Cold
Fill system to 1.0 Bar
Menu
Water Pressure 2/3
Bleed Radiators
Rell System to 1.0 Bar
Restart Menu
Water Pressure 3/3
If fault persists
Contact Installer
Restart Menu

16
9. (CONT’D) DISPLAY FUNCTIONS - FAULT MESSAGES
BOILER DISPLAY MESSAGE ACTION
Check system pressure is between 1 & 1.5 bar on the pressure gauge. Restart the appliance.
If the boiler fails to operate then pelase contact Keston (if under warranty) or alternatively a
Gas Safe Registered Engineer if outside of the warranty period. In IE contact a Registered
Gas Installer (RGII).
Overheat Lockout 1/4
With Boiler Off &
System Cold
Fill system to 1.0 Bar
Restart Menu
Overheat Lockout 2/4
Bleed Radiators
Rell System to 1.0 Bar
Restart Menu
Overheat Lockout 3/4
Check Radiator Valves
And Boiler Valves
Are Open
Restart Menu
Overheat Lockout 4/4
Restart Boiler
If Fault Persists
Contact Installer
Restart Menu

17
9. (CONT’D) DISPLAY FUNCTIONS - FAULT MESSAGES
BOILER DISPLAY MESSAGE ACTION
1. Check other gas appliances in the house are working to conrm a supply is present in
the property.
2. If other appliances fdo not work or there are not other appliances, check the gas supply is
on at the meter and/or pre payment meter has credit. If the boiler fails to operate then please
contact Keston (if under warranty) or alternatively a Gas Safe Registered Engineer if outside
of the warranty period. In IE contact a Registered Gas Installer (RGII).
1. Check other gas appliances in the house are working to conrm a supply is present in
the property.
2. If other appliances fdo not work or there are not other appliances, check the gas supply is
on at the meter and/or pre payment meter has credit. If the boiler fails to operate then please
contact Keston (if under warranty) or alternatively a Gas Safe Registered Engineer if outside
of the warranty period. In IE contact a Registered Gas Installer (RGII).
Restart the appliance - if the boiler fails to operate then please contact Keston (if under
warranty) or alternatively a Gas Safe Registered Engineer if outside of the warranty period.
In IE contact a Registered Gas Installer (RGII).
Flame Loss
Contact Installer
Menu
Ignition Lockout 1/2
Check Other Gas
Appliances Work
Restart Boiler
Restart Menu
Ignition Lockout 2/2
If Fault Persists
Contact Installer
Restart Menu
Fan Fault
Contact Installer
Restart Menu

18
9. (CONT’D) DISPLAY FUNCTIONS - FAULT MESSAGES
BOILER DISPLAY MESSAGE ACTION
Restart the appliance - if the boiler fails to operate then plese contact Keston (if under
warranty) or alternatively a Gas Safe Registered Engineer if outside of the warranty period.
In IE contact a Registered Gas Installer (RGII).
Restart the appliance - if the boiler fails to operate then plese contact Keston (if under
warranty) or alternatively a Gas Safe Registered Engineer if outside of the warranty period.
In IE contact a Registered Gas Installer (RGII).
Flow Thermistor Fault
Contact Installer
Restart Menu
Return Thermistor Fault
Contact Installer
Restart Menu

19

Keston Heating , PO Box 103, National Avenue, Kingston Upon Hull, HU5 4JN
Tel [phone] Fax [phone] Email [e-mail]
Keston Helpline: 01482 443005
www.keston.co.uk
Keston Heating pursues a policy of continuing improvement in the design and performance of its products.
The right is therefore reserved to vary specification without notice.
EVERYTHING IS POSSIBLE