BoilerFaultCodesYour boiler has shut itself down because it has detected that it is getting far too hot, usually due to a lack of water flow or a circulation blockage.
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 - Maximum temperature at the flow/return temperature sensor is too high when the safety cut-out function is operating using the NTC
What causes this fault?
This fault occurs when the boiler's internal water temperature rises too quickly or exceeds a safe limit, triggering an emergency shutdown to prevent damage. The most common reasons are a seized pump failing to move water, a buildup of sludge blocking the heat exchanger, or air trapped within the system preventing proper circulation.
This issue often appears when the heating is first turned on after summer, as circulation pumps can seize up during long periods of inactivity.
DIY fix possible
Check that your boiler pressure is between 1.0 and 1.5 bar on the digital display or gauge.Ensure all radiator valves are fully open to allow water to circulate.Try resetting the boiler by pressing the button with the flame symbol 'X' crossed out.
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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