Overview
E02 on a Keston C36 combi means the boiler has detected a flame signal it believes to be incorrect — commonly called a false flame fault. The control electronics are seeing a flame when they either expect none, or the flame signal behavior is inconsistent with normal ignition. When the boiler sees this it will usually go into lockout to prevent unsafe operation. This fault can be caused by a number of things: a faulty or contaminated flame detection electrode (or its wiring), poor electrical earthing, intermittent mains supply or low voltage, electrical noise/shorts to the control board, or a failing control (main) board. Severity is moderate to high: the boiler will normally lock out and you will lose heating and hot water until the cause is fixed. Because ignition, gas valves and control electronics are involved, repairs beyond basic checks should only be done by a Gas Safe registered engineer — it is not a DIY repair to open and work on gas parts or the PCB.
Possible Cause: False flame – possibly a problem with the power supply
Troubleshooting Steps
Safety first
- If you smell gas, do not operate the boiler: turn off the gas at the meter, get everyone out of the building, ventilate, and call the national gas emergency number immediately. Do not try to relight or reset the boiler.
- If you do any checks, avoid removing the boiler cover or touching internal components. Isolate the electrical supply before opening the appliance. Only a Gas Safe engineer should access gas-carrying parts, the burner, electrodes or replace the PCB.
Initial homeowner checks (safe, simple steps)
1) Record the fault: note E02 display and any other lights/behaviour and when it started.
2) Try one controlled reset: press the boiler reset button once and allow the boiler to attempt ignition. If it clears and stays running, monitor it for repeated occurrences. Repeated resets are not recommended; if it locks out again call an engineer.
3) Check mains/house supply: confirm other electrical items work, check the consumer unit for tripped breakers or a blown fuse that feeds the boiler. If you suspect widespread low voltage or supply issues, contact an electrician or your electricity supplier.
4) Check gas supply basics: confirm other gas appliances (hob, gas fire) work. If nothing else has gas, contact your gas supplier. Do not attempt internal gas checks yourself.
5) Check external controls: ensure room thermostat, programmer/timer and hot water demand are set correctly and not causing unexpected behaviour.
Diagnostic and likely fixes (for an engineer)
- If resets and basic checks do not clear the fault, call a Gas Safe engineer. What they will typically do:
1) Confirm the fault and view fault history/logs on the boiler display.
2) Verify mains voltage and earth continuity to rule out supply or earthing problems.
3) Inspect the flame detection electrode and high-tension lead for contamination, damage or incorrect position; clean or replace if required.
4) Check wiring and connectors between electrode and control board for loose connections or short circuits.
5) Verify ignition spark generation and correct gas valve operation; measure inlet gas pressure at the valve (typical reference ~20 mbar) and check for correct gas supply to the appliance.
6) Test the flame sensing circuit input to the PCB. If the sensor input or PCB behaves abnormally the main control board may need repair/replacement.
7) Investigate possible electrical noise or interference that could create a false flame signal (e.g. nearby electrical faults, poor earthing, swapped wires).
- Common engineer remedies include repositioning/cleaning or replacing the flame probe, repairing wiring, correcting earthing, replacing a faulty main control PCB or replacing a damaged gas valve/ignition component. The exact repair depends on measured tests.
When to call a professional
- Call a Gas Safe registered engineer if the reset does not clear the fault, if the fault returns, if you suspect a supply issue you cannot fix, or if you detect any gas smell or unsafe condition. Do not attempt internal repairs or PCB/gas component replacements yourself.
What to tell the engineer
- Give them the exact fault code (E02), what you tried (one reset, whether other gas appliances work, any tripped breakers, whether fault is intermittent or constant), and any relevant history (power cuts, storms, recent work to the system).
Final note
- E02 can be intermittent but may point to a failing sensor or control board. Because ignition and gas control are involved, professional diagnosis and repair are required for safety and correct restoration of service.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Keston C36 Combi Gas Boiler.