Boiler shows 111, will not fire, fan may not start

Critical safety: Flue faults can lead to carbon monoxide risk. If you suspect flue blockage, turn off the boiler and do not use it until checked by a Gas Safe engineer.

• Visual flue check (external only): Inspect the flue terminal outside for obstructions such as leaves, nests, or ice. Do not dismantle the flue yourself.
• Check fan operation: Listen for the flue fan starting when there is a demand. If silent, the fan or its wiring may be faulty.
• Flue thermostat reset: Some models have a manual reset flue stat. With power off, an engineer can access and reset it after confirming safe operation.
• Do not bypass safety devices: Never bridge or bypass thermostats or safety switches. If 111 persists, a qualified engineer must inspect the flue, fan, and thermostat.