BoilerFaultCodesYour boiler has shut down because the water is heating up too quickly or hasn't been able to circulate correctly through 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: Maximum delta temperature
What causes this fault?
This fault occurs when the internal sensors detect that water inside the boiler is getting too hot too quickly, or there is too large a temperature difference between the water leaving and returning to the unit. The most common reason is a lack of water flow, often caused by a failing pump or a blockage in the pipework that prevents heat from being carried away to your radiators. It can also be triggered if the sensors themselves become faulty and provide inaccurate temperature readings to the control board.
This fault is frequently seen at the start of autumn when heating systems are turned back on after a long summer break, which can cause internal pump components to seize.
DIY fix possible
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barSwitch the boiler off and back on again to reset the system
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A boiler cover plan would cover faults like F26 — no call-out fees, no surprises.
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