Error 3 flashes green

Safety precautions:

1) If you smell gas, stop immediately: do not operate electrical switches, do not use phones inside the property, open windows and doors to ventilate, turn off the gas supply at the meter if safe to do so, evacuate everyone from the building and call the gas emergency number immediately.

2) If you are unsure or uncomfortable at any point, call a Gas Safe registered engineer. Do not attempt internal gas or electrical repairs yourself.

Initial checks a homeowner can do:

1) Confirm gas supply: check other gas appliances (hob, oven) are working. If nothing works, contact your gas supplier. If you have a prepayment meter, check there is credit.

2) Check the boiler gas isolation valve (usually a lever on the incoming gas pipe) is in the open position (lever parallel to the pipe).

3) Check the flue terminal outside for obvious blockages (birds' nests, leaves, snow) and clear anything obvious and safe to remove. Do not stick objects into the flue.

4) In cold weather, check the external condensate pipe for ice. If frozen, thaw with warm (not boiling) water until it flows freely.

5) Check the boiler display/LEDs for lockout indication. Note the code and the exact flash pattern; write it down for an engineer.

6) Check mains electrical supply to the boiler and that the boiler is switched on. Verify system pressure is roughly 1–1.5 bar (useful general check though not the primary cause of flame loss).

Reset and observe (safe basic diagnostic):

1) Try a controlled reset once: locate the reset button or the selector switch marked R on the control panel. Hold the reset for the time specified by your model (typically 5–10 seconds) and release.

2) Watch and listen: you should hear the fan start, the ignition attempts (clicking), and the gas valve operate. The boiler will try to establish a flame — if it lights and stays on, monitor the boiler for a while to ensure it stays lit and the fault does not recur.

3) Do not repeatedly reset the boiler. If the same fault returns after one or two resets, stop and call a professional.

If the fault persists after basic checks and a reset:

1) Do not attempt to remove covers or work on gas components. The likely causes beyond homeowner checks include a faulty ionisation probe/electrode, damaged ignition lead, failed gas valve, blocked injector, fan or air pressure switch failure, or PCB/communication fault.

2) Record exact fault indications, times, and any conditions (cold weather, after a power cut, after topping up pressure) to give the engineer useful diagnostic information.

3) Arrange for a Gas Safe registered engineer to attend. Tell them it is a flame loss fault (three green flashes) and give them the observations you made. They will have the tools and certification to safely test gas pressure, inspect and replace ignition electrodes, test the gas valve and PCB, and check flue and condensation systems.

Final notes:

1) Flame loss is a safety shutdown — treat it seriously. If at any time you detect gas smell or other unsafe signs, call emergency services/gas emergency first.

2) Basic checks (gas supply, prepayment credit, isolation valve, flue blockage, frozen condensate, single reset) are appropriate for a homeowner. All internal diagnostics and repairs must be done by a Gas Safe registered engineer.