BoilerFaultCodesYour boiler's pilot light is on, but the main heating burner is failing to ignite because the temperature control switch is broken or incorrectly reading the heat levels.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical 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 fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like C.(4) — no call-out fees, no surprises.
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Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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