BoilerFaultCodesYour boiler has detected that the water is heating up too quickly or not circulating properly through the system, causing a large temperature gap between the pipes.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: There is excessive temperature difference between the flow and return thermistors.
What causes this fault?
This fault occurs when the water inside the boiler heats up much faster than it can be moved away, leading to a dangerous heat buildup. The most common reasons are a failed pump that isn't pushing water round or a blockage in the heat exchanger, such as a buildup of sludge or limescale. In some cases, it may simply be that the internal sensors have become faulty and are providing incorrect temperature readings to the control board.
This fault is more frequent in autumn when heating systems are first turned on after summer, as pumps can seize 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 bar on the pressure gaugeBleed all radiators to remove trapped air that could be blocking water flow
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A boiler cover plan would cover faults like 24 — no call-out fees, no surprises.
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