Boiler shows code 3, fan running but no ignition, boiler does not fire

Warning: Ignition and gas valve checks involve gas and combustion. Do not remove the boiler case or attempt internal repairs unless you are a Gas Safe registered engineer.

• Reset the boiler: Turn the boiler off at the control panel, wait 10 seconds, then turn it back on. If code 3 persists and the boiler never progresses to flame, note any error codes that follow.
• Check gas supply: Ensure the gas meter is on and that other gas appliances (e.g. hob) work. If there is no gas supply, contact your gas supplier.
• Check flue terminal: From outside, visually inspect the flue terminal for obstructions (leaves, nests, debris). Do not insert objects into the flue. Clear any obvious external blockage.
• Power cycle: Isolate power at the fused spur for 30 seconds, then restore. Sometimes the PCB will reset and complete ignition.
• Call an engineer: If the boiler repeatedly stalls at code 3, a Gas Safe engineer must check the ignition electrode, flame sensor, gas valve operation, fan speed, and flue integrity.