BoilerFaultCodesYour boiler has shut down because it has detected it is getting too hot, usually caused by a lack of water flow or a blockage in 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: Safety switch off temperature limiter
What causes this fault?
This fault occurs when the boiler's internal heat exchanger reaches an unsafe temperature, forcing the system to shut down to prevent damage. The most common reasons are a lack of water flow caused by a broken internal pump, or a blockage in the pipes resulting from a build-up of sludge and debris.
This fault is more common when turning your heating back on for the first time in autumn, as circulation pumps can seize up after sitting idle during the summer months.
DIY fix possible
Check if your radiator valves are openCheck the boiler pressure gauge and top up if it is below 1.0 barPress the reset button (flame symbol) to see if the fault clears
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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