BoilerFaultCodesYour boiler has detected that the water temperature is rising too quickly, which usually means the water isn't flowing through the system properly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Maximum temperature rise slope
What causes this fault?
This fault occurs when the internal sensors detect the heat exchanger is getting too hot, too fast. It usually means the water is trapped or moving too slowly to carry the heat away, often caused by a failing pump or a blockage in the system pipes. Essentially, the boiler is producing heat but has nowhere for it to go, so it shuts down to prevent damage.
This fault is more common when the heating is first switched on after summer, as pump components can seize up during long periods of inactivity.
DIY fix possible
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barBleed all radiators to remove trapped air from the system
Find a Gas Safe engineer
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A boiler cover plan would cover faults like F25 — 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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