BoilerFaultCodesTechnical description
Main burner fails to light, pilot burning - Thermostat out of calibration or faulty.
What causes this fault?
This fault occurs when the internal temperature sensor fails to signal the main burner to ignite, even though the pilot light is ready and waiting. The most common reason is that the thermostat has lost its calibration or its sensing bulb has degraded, meaning it can no longer accurately tell the boiler that the water has cooled down and needs reheating.
This issue often becomes apparent during the first cold spell of autumn when the thermostat is suddenly required to cycle on and off more frequently after being idle all summer.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.