BoilerFaultCodesYour boiler is shutting itself down because exhaust fumes are not escaping correctly through the chimney, which could cause dangerous gases to enter your home.
Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now — this fault can be dangerous if ignored.
Technical description: If the flue becomes blocked or is subjected to adverse conditions the safety thermostat will operate and shut down the boiler. The Burner On neon will extinguish. If the blockage or adverse condition persists the safety thermostat will continue to operate and cycle the boiler on and off.
What causes this fault?
This fault occurs when the safety sensor detects that harmful exhaust gases are not moving freely up the chimney and are instead backing up into the boiler area. The most common reasons are a physical blockage in the flue, such as a bird's nest or debris, or severe atmospheric pressure pushing air back down the chimney. Because these gases contain carbon monoxide, the boiler automatically shuts down to prevent them from entering your living space.
This issue is more frequent during periods of high winds or extreme cold, which can create downdraughts or 'air plugs' in the chimney that prevent exhaust fumes from rising.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like Flue Safety Thermostat (Cycling) — no call-out fees, no surprises.
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