BoilerFaultCodesYour boiler has switched itself off because it has reached an unsafe temperature and needs to cool down.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Safety switch-off: Temperature limiter
What causes this fault?
This fault occurs when the boiler's internal sensors detect that the water temperature has risen too quickly or exceeded a safe limit, triggering an emergency shutdown to prevent damage. The most common cause is a lack of water circulation, often due to a seized pump, a blockage in the pipework, or air trapped within the heat exchanger.
This fault is more common when the heating is first turned on after summer, as pump components can seize up during long periods of inactivity.
DIY fix possible
Ensure all radiator valves are fully open to allow water to flow.Check the boiler pressure gauge and top up to 1.5 bar if it is too low.Press the 'Flame' or 'Reset' button and hold for one second to restart the system.
Find a Gas Safe engineer
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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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