If you’re experiencing problems with your Keston boiler, this guide to Keston boiler fault codes can help you identify the issue and understand your next steps.
Keston Heating has a long history in the UK heating industry, originally established in 1928 to provide domestic and commercial heating solutions. In 2006, the brand was acquired by Ideal Heating, one of the most trusted names in the industry. By 2013, Keston boiler production had moved to Ideal’s state-of-the-art facility in Hull, bringing improved reliability and support to the Keston range.
While Keston’s Trustpilot rating currently stands at 2.3 out of 5 stars from a limited number of reviews, many negative comments focus on past aftersales experiences rather than the boilers’ performance. It’s important to note that most of these reviews pre-date the Ideal Heating acquisition.
Customer satisfaction has improved significantly since the rebrand and support transition to Ideal Heating. Ideal holds a 4.8-star Trustpilot rating from over 57,600 reviews, demonstrating a commitment to quality service and customer care.
Thanks to their twin flue system, Keston boilers are particularly popular in compact properties and flats, especially in urban areas like London. This flexible system allows the flue to be extended up to 27 metres, horizontally or vertically, making installation possible in tight or unusual spaces.
New Keston boilers come with an up to 7-year warranty and are compatible with a range of controls and accessories, including the Keston System Filter, RF Electronic Programmable Room Thermostat, and Mechanical Timer, helping you get the most out of your heating system.
While WarmZilla does not currently stock Keston boilers, we offer a wide selection of high-performance alternatives from trusted brands. If you’re considering a replacement, use our quick and easy online boiler survey to find the right boiler for your home. It only takes a few minutes to receive personalised recommendations.
Remember, WarmZilla offers a Best Price Guarantee. If you find a cheaper boiler quote elsewhere, we’ll beat it by £50.
Keep reading for a full list of Keston boiler error codes and their meanings. This will help you better understand what’s going wrong and discuss it confidently with your Gas Safe engineer.
C36 Combi Gas Boiler Error Codes
| Fault Code | Possible Cause |
|---|---|
| E01 | Ignition failure – the boiler has attempted to light 5 times and not succeeded – check the gas supply is on |
| E02 | False flame – possibly a problem with the power supply |
| E03 | Boiler overheat – check that any valves to the heating circuit have not been shut down, no air in the system and that the water pressure is correct |
| E05 | Fan failure – boiler cannot detect fan rotation – check fan operation and both connectors onto fan |
| E07 | Flue overheat – check combustion and flue temperature vs. return temperature – the flue temperature should be no more than 10°C above return temperature. Possible heat exchanger fault. |
| E08 | Flame circuit error – possible control box fault |
| E09 | Valve drive error – possible gas valve or control box fault |
| E10 | Control box errors – possible faulty control box |
| E11 | The automatic test for calibration of flow and return sensors has failed – check both flow and return sensors are located on the correct pipes and are producing the correct readings |
| E12 to E22 | Control box errors – possible faulty control box |
| E23 | Water filling error – check water pressure sensor |
| E24 | Water pressure lost 4 times in 24 hours – possible leak, check system and boiler |
| E25 | Control box errors – possible faulty control box |
| E26 | Flame drop out – check for obstruction of the flue and/or air terminals, blockage/freezing of the drain pipe or a low gas supply (LPG) |
| E30 | Flow sensor short circuit – check connections to flow sensor |
| E31 | Flow sensor open circuit – check connections to flow sensor are in place |
| E32 | DHW sensor short circuit – check connections to domestic hot water (DHW) sensor |
| E33 | Domestic hot water (DHW) sensor short circuit – check connections to DHW sensor are in place |
| E34 | Mains supply voltage < 180V – may be a problem with your power supply |
| E35 | Mains supply frequency incorrect – may be a problem with the power supply |
| E37 | Water pressure error – increase the system water pressure |
| E38 | Reset key fault – replace fascia PCB |
| E40 | Water pressure too high |
| E41 | Communication error between fascia and control box – check cables |
| E43 | Return sensor short circuit – check connections to return sensor |
| E44 | Return sensor open circuit – check connections to return sensor are in place |
| E45 | Flue sensor short circuit – check connections to flue sensor |
| E46 | Communication error between fascia and control box – check cables |
| E99 | Flue sensor short circuit – check connections to flue sensor are in place |
S30 System Gas Boiler Error Codes
| Fault Code | Possible Cause |
|---|---|
| 0 | The boiler is in standby mode awaiting either a central heating call or hot water demand |
| C | The boiler has a call for central heating / hot water but the appliance has reached the desired temperature set on the boiler |
| C and Burner Light | The boiler is operating for central heating / hot water |
| F and Burner Light | The boiler is operating in frost mode |
| F0 | Boiler Chip Card (BCC) not fitted |
| F6 | Outside sensor failure |
| F7 | Low mains voltage |
| F9 | Printed circuit board (PCB) Fault |
| L5 | 5 boiler resets in 15 minutes |
| L6 | False flame lockout |
| C0 | Boiler Chip Card (BCC) activation fault |
| C2 | Boiler Chip Card (BCC) fault |
| F1 | Low water pressure |
| L1 | Flow temperature overheat |
| F2 | Flame loss |
| L2 | Flame loss |
| F3 | Fan fault |
| F4 | Control / No flow thermistor |
| F5 | Return thermistor |
C40 C55 Combi Gas Boiler
| Fault Code | Possible Cause |
|---|---|
| Enn | Fault causing a boiler shutdown |
| E00 | Flame detected when not expected – check boiler earth and probe condition |
| E02 | No ignition after restart – check gas supply, gas valve operation and ignitor electrode spark generation |
| E03 | Gas valve faulty or not connected |
| E04 | Power has been reset whilst boiler was in lockout |
| E11 | Internal electronics error – reset or replace control box |
| E18 | Flow overheat – check water circulation |
| E19 | Maximum return temperature exceeded – check circulation |
| E25 | Flow temperature increased too quickly – check water circulation |
| E30 | Difference between flow and return temperatures too high – check circulation |
| E31 | Flow thermistor short circuit – check/replace connections/thermistor |
| E32 | Return thermistor short circuit – check/replace connections/thermistor |
| E36 | Flow thermistor open circuit – check/replace connections/thermistor |
| E37 | Return thermistor open circuit – check/replace connections/thermistor |
| E44 | Low water pressure |
Boiler Manuals
Thanks to our friends over at Freeboilermanuals.com, we have listed all the manuals for Keston boilers below in case you need further information about your boiler.
- Keston Celsius 25
- Keston C36 combi
- Keston C36P combi
- Keston C45
- Keston C40P
- Keston C55
- Keston C55P
- Keston C90
- Keston C110
- Keston 30C
- Keston Combi C30
- Keston Combi C35
- Keston Heat 45
- Keston Heat 55
- Keston Heat 45P
- Keston Heat 55P
- Keston Heat 2 45
- Keston Heat 2 55
- Keston Heat 2 45P
- Keston Heat 2 55P
- Keston System S30
- Keston Thermomatic RSM 20 FB combi
- Keston K130
- Keston Qudos 28H
- Keston Qudos 28HP
- Keston Qudos 28S
- Keston Qudos 28SP
- Keston Qudos 37
- Keston Qudos 37P
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