BoilerFaultCodesYour boiler has detected that the water inside is getting too hot because it isn't moving through the system quickly enough.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flow temperature too high: check system flow and pump.
What causes this fault?
This fault occurs when the heat generated by the burner cannot be transferred away from the boiler fast enough, causing the internal water temperature to spike safely out of range. The most common reasons are a failing circulation pump that isn't pushing water through the pipes, or a blockage caused by a buildup of sludge and debris within the system.
This issue is most frequently seen in autumn when heating is switched back on after a summer of inactivity, which can cause internal pump components to seize.
DIY fix possible
Check that at least two or three radiators have their valves turned fully openEnsure the external pump (if visible) is vibrating or hummingCheck that the system pressure gauge is between 1.0 and 1.5 barWait for the boiler to cool down and press the 'Reset' button
Find a Gas Safe engineer
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A boiler cover plan would cover faults like E18 — 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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