BoilerFaultCodesYour boiler has switched itself off because the internal exhaust gases have reached a temperature that is too high, often caused by a circulation problem or a lack of water.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flue gas overheat fault
What causes this fault?
This fault occurs when the sensors detect that the exhaust gases leaving the boiler are getting much hotter than they should be, triggering an automatic safety shutdown. The most common reason is that heat isn't being moved away from the burner quickly enough, usually due to a lack of water pressure, a failing pump, or a blockage in the main heat exchanger.
DIY fix possible
Check the boiler pressure gauge and top it up to 1.5 bar if it is too lowEnsure all radiator valves are fully open to allow water to flowTry resetting the boiler once the system has cooled down
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like F25 — no call-out fees, no surprises.
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Glow-worm Ultracom 24cx 30cx is discontinued — time for a new one?
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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