BoilerFaultCodesYour boiler has switched itself off because it has become too hot inside, likely due to a circulation issue or a temporary blockage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Overheat thermostat tripped
What causes this fault?
This fault occurs when the internal temperature of the boiler exceeds safe limits, triggering a safety switch to prevent damage. The most common reasons are a pump failure that stops water from moving or a buildup of debris and limescale that restricts flow through the heat exchanger.
This issue often surfaces in autumn when the heating is turned back on after a long summer break, as internal pump components can become seized from inactivity.
DIY fix possible
Check that your radiator valves are open to allow water to flow.Check your boiler pressure gauge and top it up to 1.5 bar if it is too low.Let the boiler cool down for 30 minutes, then press the 'Reset' button (the flame symbol with a cross).
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 F5 — 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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