BoilerFaultCodesYour boiler has switched itself off because the internal water temperature has become too hot, usually caused by a lack of water flow through the system.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flow Temperature Overheat Lockout
What causes this fault?
This fault occurs when the water inside the boiler exceeds a safe temperature, causing the system to shut down for safety. The most common reasons are a pump failure preventing water from moving through the system or a blockage caused by a build-up of sludge and debris. It can also be triggered by a faulty sensor that is incorrectly reporting the water temperature to the control board.
This fault is more common in autumn when homeowners turn their heating back on after a long summer break, as the internal pump can often become seized or stuck during periods of inactivity.
DIY fix possible
Check that your radiator valves are fully openEnsure your boiler pressure is between 1 and 1.5 bar on the gaugeReset the boiler by turning the control knob to 'RE' or pressing the reset button
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 L1 — 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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