BoilerFaultCodesYour boiler has sensed an unusual temperature difference between the water leaving it and the water returning, suggesting that water is not circulating through your heating system correctly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Different flow/return temperatures
What causes this fault?
This fault occurs when the boiler detects that heat is not being carried away from the unit quickly enough, often due to a pump failure or a blockage in the pipework. It physically happens because the water exiting the boiler is significantly hotter than the water coming back, suggesting the flow has slowed down or stopped entirely. The most common reasons are a seized circulation pump or a buildup of sludge and debris within the main heat exchanger.
This issue often surfaces at the start of autumn when heating systems are turned back on after sitting idle all summer, which can cause internal pump components to seize.
DIY fix possible
Check that all radiator valves (TRVs) are fully openEnsure your system pressure is topped up to roughly 1.5 barBleed all radiators to remove trapped air locksRestart the boiler using the reset button
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A boiler cover plan would cover faults like E41 — 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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