BoilerFaultCodesYour boiler is heating up too quickly, causing it to shut down to prevent damage from overheating.
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 boiler's internal sensors detect that the water temperature is rising much faster than it should. The most common reason is that water isn't moving through the system quickly enough, often due to a failing pump or a buildup of debris and sludge that creates a blockage. Because the heat cannot be carried away to your radiators, the boiler shuts down to prevent itself from overheating and becoming damaged.
This issue often surfaces in autumn when the central heating is switched back on after a summer of inactivity, which can cause internal pump components to seize.
DIY fix possible
Check that all radiator valves are fully openEnsure the central heating system pressure is between 1.0 and 1.5 barBleed all radiators to remove trapped air that might be blocking water flow
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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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.
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