BoilerFaultCodes E 01 Your boiler is failing to light the flame needed to produce heat or hot water.
Your boiler is failing to light the flame needed to produce heat or hot water.
Parts commonly replaced
- Ignition electrode
- Gas valve
- PCB
Keston C36 Fault codes & diagnostics
30 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
System Natural Gas 36 kW 2013-2019 Discontinued
Replaced by: Keston System 36
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Severity at a glance
Each cell = one fault code. Hover to identify. 29 High
1 Medium
Just want the most common Keston C36 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 30 documented codes
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E02 Your boiler thinks a flame has started when it shouldn't have, usually caused by an electrical glitch or a faulty sensor signal.
Your boiler thinks a flame has started when it shouldn't have, usually caused by an electrical glitch or a faulty sensor signal.
Parts commonly replaced
- Flame sense electrode
- Printed Circuit Board (PCB)
- Ionisation lead
Related codes
E03 Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.
Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.
What to check first
- Check that the boiler pressure is between 1.0 and 1.5 bar on the gauge.
- Ensure all radiator valves and internal isolation valves are fully open.
- Bleed your radiators to remove any trapped air pockets from the system.
Parts commonly replaced
- Circulation Pump
- Overheat Thermostat
- Thermistor (NTC Sensor)
Related codes
E04 Your boiler has stopped working because the internal fan, which safely clears exhaust fumes, is not spinning or cannot be detected by the system.
Your boiler has stopped working because the internal fan, which safely clears exhaust fumes, is not spinning or cannot be detected by the system.
Parts commonly replaced
- Fan assembly
- Wiring harness
- Main PCB
Related codes
E05 Your boiler has stopped working because the internal fan, which safely exhausts fumes, is not spinning correctly or cannot be detected by the system.
Your boiler has stopped working because the internal fan, which safely exhausts fumes, is not spinning correctly or cannot be detected by the system.
Parts commonly replaced
- Fan assembly
- Main PCB
- Wiring harness
Related codes
E07 Your boiler has shut down because the internal exhaust gases are getting too hot, which is usually caused by a circulation problem or a buildup of debris inside the main heating component.
Your boiler has shut down because the internal exhaust gases are getting too hot, which is usually caused by a circulation problem or a buildup of debris inside the main heating component.
Parts commonly replaced
- Main Heat Exchanger
- Heat Exchanger Graphite Seal
- Flue Thermistor
- Burner Door Insulation
Related codes
E08 Your boiler is having trouble managing the flame and electrical signals, which is preventing it from heating your home safely.
Your boiler is having trouble managing the flame and electrical signals, which is preventing it from heating your home safely.
Parts commonly replaced
- Main PCB (Control Board)
- Flame Sensing Electrode
- Wiring Harness
Related codes
E09 Your boiler has detected an internal communication problem between its electronic brain and the gas supply system, meaning it cannot safely light the flame.
Your boiler has detected an internal communication problem between its electronic brain and the gas supply system, meaning it cannot safely light the flame.
Parts commonly replaced
- Gas Valve
- Printed Circuit Board (PCB)
- Wiring Harness
Related codes
E10 Your boiler’s internal computer has encountered a critical electronic failure and cannot safely operate the system.
Your boiler’s internal computer has encountered a critical electronic failure and cannot safely operate the system.
Parts commonly replaced
- Main PCB (Control Board)
- Wiring harness
Related codes
E11 Your boiler has stopped working because its internal sensors are reporting conflicting temperature readings that don't match up during a self-test.
Your boiler has stopped working because its internal sensors are reporting conflicting temperature readings that don't match up during a self-test.
Parts commonly replaced
- Flow NTC sensor
- Return NTC sensor
- Wiring loom
Showing 11–20 of 30
E12 to E22 Your boiler’s internal computer has encountered a critical error and can no longer control the heating process safely.
Your boiler’s internal computer has encountered a critical error and can no longer control the heating process safely.
Parts commonly replaced
- Main Control PCB
- Display PCB
E23 Your boiler has stopped working because it cannot correctly detect the water pressure, often due to a low water level or a faulty sensor.
Your boiler has stopped working because it cannot correctly detect the water pressure, often due to a low water level or a faulty sensor.
What to check first
- Check the pressure gauge on the front of the boiler
- If the pressure is below 1 bar, use the filling loop to top it up to 1.5 bar
- Reset the boiler by pressing the 'Reset' button
Parts commonly replaced
- Water pressure sensor
- Pressure switch
- Wiring harness
Related codes
E24 Your boiler has shut down because it keeps losing water pressure and likely has a leak somewhere in the heating system or the unit itself.
Your boiler has shut down because it keeps losing water pressure and likely has a leak somewhere in the heating system or the unit itself.
What to check first
- Check for visible water leaks under the boiler and around your radiators or valves.
- Top up the system pressure to 1.5 bar using the external filling loop.
- Reset the boiler and monitor if the pressure drops again.
Parts commonly replaced
- Expansion Vessel
- Pressure Relief Valve
- Automatic Air Vent
Related codes
E25 Your boiler's internal computer has encountered a critical error and cannot safely operate the system.
Your boiler's internal computer has encountered a critical error and cannot safely operate the system.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Control Box Unit
Related codes
E26 Your boiler is struggling to keep its flame lit, which often happens because the drainage pipe is blocked or frozen, or there is an issue with the air supply.
Your boiler is struggling to keep its flame lit, which often happens because the drainage pipe is blocked or frozen, or there is an issue with the air supply.
What to check first
- Check the white plastic condensate pipe outside for signs of ice or blockages.
- If frozen, gently pour warm (not boiling) water over the pipe to thaw it.
- Ensure the external flue terminal is not obstructed by debris or garden foliage.
Parts commonly replaced
- Flame Sensing Electrode
- Gas Valve
- Condensate Trap
Related codes
E30 Your boiler has detected an electrical fault with the internal sensor that monitors water temperature, causing the system to stop working for safety.
Your boiler has detected an electrical fault with the internal sensor that monitors water temperature, causing the system to stop working for safety.
Parts commonly replaced
- Flow thermistor (NTC sensor)
- Wiring harness
- Main PCB
Related codes
E31 Your boiler has lost communication with the internal sensor that monitors the temperature of the water leaving the unit, usually due to a loose wire or a faulty part.
Your boiler has lost communication with the internal sensor that monitors the temperature of the water leaving the unit, usually due to a loose wire or a faulty part.
Parts commonly replaced
- Flow Thermistor
- Wiring Harness
- Main PCB
Related codes
E32 Your boiler has lost its ability to regulate hot water temperature correctly because of a wiring or sensor fault, meaning you likely have no hot water.
Your boiler has lost its ability to regulate hot water temperature correctly because of a wiring or sensor fault, meaning you likely have no hot water.
Parts commonly replaced
- Domestic Hot Water (DHW) Thermistor
- Wiring harness
Related codes
E33 Your boiler is having trouble measuring the temperature of your hot water because of a faulty internal sensor or a wiring issue.
Your boiler is having trouble measuring the temperature of your hot water because of a faulty internal sensor or a wiring issue.
Parts commonly replaced
- DHW Thermistor (NTC Sensor)
- Wiring harness
Related codes
E34 Your boiler has stopped working because it isn't receiving enough electricity from your home's power supply to run safely.
Your boiler has stopped working because it isn't receiving enough electricity from your home's power supply to run safely.
What to check first
- Check if other appliances in your home are flickering or underperforming
- Ensure your fuse box / consumer unit has not partially tripped
- Contact your electricity network provider to see if there is a brownout or power fluctuation in your area
Parts commonly replaced
- No parts usually required
- Printed Circuit Board (PCB) - if damaged by surge
Related codes
Showing 21–30 of 30
E35 Your boiler is struggling to detect a stable electrical signal from the mains power supply, causing it to shut down as a safety precaution.
Your boiler is struggling to detect a stable electrical signal from the mains power supply, causing it to shut down as a safety precaution.
Parts commonly replaced
- Printed Circuit Board (PCB)
- External power supply/wiring
Related codes
E37 Your boiler has detected that the water pressure is too low, which has caused it to stop working to avoid damage.
Your boiler has detected that the water pressure is too low, which has caused it to stop working to avoid damage.
What to check first
- Locate the filling loop (usually a silver flexible hose) underneath the boiler.
- Open the taps on the filling loop slowly until you hear water entering the system.
- Watch the pressure gauge and close the taps once the needle reaches 1.5 bar.
Parts commonly replaced
- Filling loop
- Expansion vessel
- Pressure sensor
Related codes
E38 Your boiler's control panel has developed a mechanical or electrical fault with the reset button, meaning it cannot process your commands correctly.
Your boiler's control panel has developed a mechanical or electrical fault with the reset button, meaning it cannot process your commands correctly.
Parts commonly replaced
- Fascia PCB
- User Interface Control Board
Related codes
E40 Your boiler has switched off because there is too much water pressure in the system, which can put unnecessary strain on the internal seals.
Your boiler has switched off because there is too much water pressure in the system, which can put unnecessary strain on the internal seals.
What to check first
- Check that the filling loop valves are fully closed
- Switch off the boiler and allow it to cool
- Bleed water from a radiator using a bleed key into a container
- Monitor the pressure gauge until it returns to between 1.0 and 1.5 bar
Parts commonly replaced
- Filling loop valve
- Expansion vessel
- Pressure relief valve
Related codes
E41 Your boiler's main control panel is having trouble talking to the internal computer, which is preventing the system from starting up.
Your boiler's main control panel is having trouble talking to the internal computer, which is preventing the system from starting up.
Parts commonly replaced
- Wiring harness
- Display fascia
- Main PCB
Related codes
E43 Your boiler has detected an electrical fault with the internal sensor that monitors the temperature of the water returning to the unit, causing it to shut down for safety.
Your boiler has detected an electrical fault with the internal sensor that monitors the temperature of the water returning to the unit, causing it to shut down for safety.
Parts commonly replaced
- Return thermistor (NTC sensor)
- Sensor wiring harness
Related codes
E44 Your boiler has lost communication with the sensor that monitors water returning from your radiators, often causing the system to stop working as a safety precaution.
Your boiler has lost communication with the sensor that monitors water returning from your radiators, often causing the system to stop working as a safety precaution.
Parts commonly replaced
- Return thermistor (NTC sensor)
- Wiring harness
Related codes
E45 Your boiler has detected an electrical fault with the sensor that monitors exhaust gases, causing the system to shut down for safety.
Your boiler has detected an electrical fault with the sensor that monitors exhaust gases, causing the system to shut down for safety.
Parts commonly replaced
- Flue gas sensor (NTC)
- Wiring harness
- Main control board
Related codes
E46 Your boiler's main control panel has lost connection with the internal computer that runs it, meaning the boiler cannot receive commands.
Your boiler's main control panel has lost connection with the internal computer that runs it, meaning the boiler cannot receive commands.
Parts commonly replaced
- Wiring Harness
- Display Fascia PCB
- Main Control Board
Related codes
E99 Your boiler has detected an electrical fault with the sensor that monitors the temperature of the exhaust gases, causing the system to shut down for safety.
Your boiler has detected an electrical fault with the sensor that monitors the temperature of the exhaust gases, causing the system to shut down for safety.
Parts commonly replaced
- Flue Gas Thermistor
- Wiring Harness