BoilerFaultCodesYour boiler has shut down because the internal water has become too hot, usually because it isn't moving through the pipes properly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flow overheat – check water circulation
What causes this fault?
This fault happens when the water inside the boiler reaches a dangerously high temperature because it is unable to circulate around your radiators or hot water system. The most common reasons are a failed internal pump that has stopped spinning or a buildup of sludge and debris that is physically blocking the pipework. In some cases, the sensor that monitors temperature may simply be faulty and giving an incorrect reading.
This issue often appears when the heating is first turned on in autumn, as circulation pumps can seize up after being idle throughout the summer months.
DIY fix possible
Check that your home's radiator valves are fully open.Ensure the boiler pressure gauge is between 1 and 1.5 bar.Try resetting the boiler to see if the fault clears.
Find a Gas Safe engineer
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Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like E18 — 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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