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2023 Keston Boiler Error & Fault Codes


A Keston boiler error code will require an inspection of the problem identified by the code. There are various codes and steps that need to be followed in order to identify the exact problem with the boiler from a more extensive list of problems. The Keston error code guide will help you familiarize yourself with the simplest to most difficult boiler error codes, so you know what steps to take next.

When diagnosing a problem with Keston boilers, it is very important to first identify the error code that displays on the LEDs. The error code will indicate where the fault lies within the boiler or system and grant engineers will send out an engineer to take a look at it. The engineers are highly trained and they will identify the fault and resolve it in an efficient manner.

C36 Combi Gas Boiler Error Codes


Keston combi boiler error codes are an important part of your boiler maintenance. If you don't check your Keston C36 combi boiler error codes, you may end up with problems down the line. Error codes will help to prevent costly breakdowns and unexpected bills. In this table we'll teach you how to manually read your fault code and give you some top tips on what to do if you have any problems identifying the code.

Fault Code Possible Cause
E01Ignition failure – the boiler has attempted to light 5 times and not succeeded – check the gas supply is on
E02False flame – possibly a problem with the power supply
E03Boiler 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
E05Fan failure – boiler cannot detect fan rotation – check fan operation and both connectors onto fan
E07Flue overheat – check combustion and flue temperature vs. return temperature – the flue temperature should be no more than 10C above return temperature. Possible heat exchanger fault.
E08Flame circuit error – possible control box fault
E09Valve drive error – possible gas valve or control box fault
E10Control box errors – possible faulty control box
E11The 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 E22Control box errors – possible faulty control box
E23Water filling error – check water pressure sensor
E24Water pressure lost 4 times in 24 hours – possible leak, check system and boiler
E25Control box errors – possible faulty control box
E26Flame drop out – check for obstruction of the flue and/or air terminals, blockage/freezing of the drain pipe or a low gas supply (LPG).
E30Flow sensor short circuit – check connections to flow sensor
E31Flow sensor open circuit – check connections to flow sensor are in place
E32DHW sensor short circuit – check connections to domestic hot water (DHW) sensor
E33Domestic hot water (DHW) sensor short circuit – check connections to DHW sensor are in place
E34Mains supply voltage < 180V – may be a problem with your power supply
E35Mains supply frequency incorrect – may be a problem with the power supply
E37Water pressure error – increase the system water pressure
E38Reset key fault – replace fascia PCB
E40Water pressure too high
E41Communication error between fascia and control box – check cables
E43Return sensor short circuit – check connections to return sensor
E44Return sensor open circuit – check connections to return sensor are in place
E45Flue sensor short circuit – check connections to flue sensor
E46Communication error between fascia and control box – check cables
E99Flue sensor short circuit – check connections to flue sensor are in place

S30 System Gas Boiler Error Codes


Keston S30 System Gas Boiler Error Codes. As boiler breakdowns can cost you money, we’ve compiled the list of error codes to help you get your boiler back up and running as quickly as possible. With the amount of time it takes for a professional engineer to come around, this is an easy way for you to be able to potentially fix issues and avoid wasting more money on call-out charges and parts.

Fault Code Possible Cause
0The boiler is in standby mode awaiting either a central heating call or hot water demand
CThe boiler has a call for central heating / hot water but the appliance has reached the desired temperature set on the boiler
CAnd Burner Light The boiler is operating for central heating / hot water
FAnd Burner Light The boiler is operating in frost mode
F0Boiler Chip Card (BCC) not fitted
F6Outside sensor failure
F7Low mains voltage
F9Printed circuit board (PCB) Fault
L55 boiler resets in 15 minutes
L6False flame lockout
C0Boiler Chip Card (BCC) activation fault
C2Boiler Chip Card (BCC) fault
F1Low water pressure
L1Flow temperature overheat
F2Flame loss
L2Flame loss
F3Fan fault
F4Control / No flow thermistor
F5Return thermistor

C40 C55 Combi Gas Boiler


Keston C40 and C55 combi boilers are widely used for space heating but also for domestic hot water when the combi boiler is used alone. One of the common faults seen in these Keston boiler is a flashing fault indication on the control panel - this boiler fault code can be very difficult to interpret.

This table explains how to decode error codes for Keston C40 Gas Combination Boilers, and the Keston C55 Gas combination boiler.

Fault Code Possible Cause
EnnFault causing a boiler shutdown
E00Flame detected when not expected – check boiler earth and probe condition
E02No ignition after restart – check gas supply, gas valve operation and ignitor electrode spark generation
E03Gas valve faulty or not connected
E04Power has been reset whilst boiler was in lockout
E11Internal electronics error – rest or replace control box
E18Flow overheat – check water circulation
E19Maximum return temperature exceeded – check circulation
E25Flow temperature increased too quickly – check water circulation
E30Difference between flow and return temperatures too high – check circulation.
E31Flow thermistor short circuit – check/replace connections/thermistor
E32Return thermistor short circuit – check/replace connections/thermistor
E36Flow thermistor open circuit – check/replace connections/thermistor
E37Return thermistor open circuit – check/replace connections/thermistor
E44Low water pressure
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Table of Contents


  1. C36 Combi
  2. S30 System
  3. C40 C55 Combi

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