BoilerFaultCodesYour boiler has switched itself off because it has detected that the water inside is getting too hot.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Safety temperature limiter by NTC activated
What causes this fault?
This fault occurs when the boiler's internal temperature rises too quickly or exceeds a safe limit, causing the system to shut down to prevent damage. The most common reasons are a lack of water flow caused by a faulty pump, a blockage in the central heating pipes, or air trapped within the heat exchanger.
This issue is frequently seen when the heating is first turned back on in autumn, as pump components can seize up after being idle throughout the summer.
DIY fix possible
Check that your radiator valves are fully openEnsure your central heating pump is running and not stuckPress the reset button (flame symbol with a cross) once the boiler 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 F.20 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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