BoilerFaultCodesYour boiler has switched itself off because it has reached an unsafe temperature to prevent internal damage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Overheat thermostat tripped
What causes this fault?
This fault occurs when the water inside the boiler gets too hot, causing a safety sensor to cut the power to prevent damage. The most common reasons are a pump failure that stops water from moving around the system or a build-up of debris that restricts flow through the heat exchanger.
This issue is more frequent during the first cold snap of winter when a pump that has been idle all summer suddenly seizes or struggles to move cold, sludge-heavy water.
DIY fix possible
Ensure all radiator valves are fully open to allow water to circulate.Wait 20 minutes for the boiler to cool down completely.Press the 'Reset' button (the flame symbol with a cross) on the boiler control panel.
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 F5 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Glow-worm Xtramax is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
Affiliate links — we may earn a commission at no extra cost to you.