BoilerFaultCodesYour boiler has detected that the water is getting hot too quickly or the temperature difference between pipes is too wide, often caused by poor water flow.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Maximum delta temperature
What causes this fault?
This fault occurs when the boiler's internal sensors detect that heat isn't being carried away from the burner fast enough, causing the unit to overheat rapidly. The most common reason is a blockage in the system or a pump failure, which prevents water from circulating through the radiators as it should.
This issue often surfaces during the first cold snap of autumn when heating systems are turned on after sitting idle for months, which can cause internal pumps to seize.
DIY fix possible
Check that all radiator valves and isolation valves are fully openEnsure there is enough water pressure by checking the boiler gauge (target 1.5 bar)Bleed all radiators to remove trapped air that might be blocking flowReset the boiler to see if the fault clears
Find a Gas Safe engineer
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A boiler cover plan would cover faults like F26 — 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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