BoilerFaultCodesYour boiler is overheating because water is not moving through the system quickly enough to carry heat away.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Temperature difference between flow and safety sensor exceeds limit
What causes this fault?
This fault occurs when the water inside the boiler heats up too quickly because it isn't circulating through your radiators or pipes as it should. The most common reasons are a failed internal pump that has stopped spinning, or a blockage caused by a buildup of sludge and debris within the main heat exchanger.
This fault often appears when heating is first turned on in autumn, as pumps can seize up after being inactive over the summer months.
DIY fix possible
Check that all radiator valves are fully openCheck that the boiler pressure is between 1 and 1.5 bar on the pressure gaugeBleed all radiators to remove trapped air that might be blocking water flow
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like D4271 — 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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