BoilerFaultCodesYour boiler has become too hot and has shut itself down as a safety precaution to prevent damage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: The primary system or the boiler has overheated. (Burner On: Slow Flashing, Flame Failure: On, Power On: On)
What causes this fault?
This fault occurs when water inside the boiler reaches an unsafe temperature, triggering a safety sensor to cut the power. It is usually caused by a failure to move heat away from the burner, often due to a broken pump or a blockage in the internal pipework. In some cases, the overheat sensor itself may have failed and is reporting a false reading.
This issue is more frequent during the first cold spell of autumn when 'sticky' pumps can fail after being left turned off throughout the summer.
DIY fix possible
Check that your radiator valves are fully open and not turned off.Ensure there is enough water pressure in the system by checking the pressure gauge (it should be between 1 and 1.5 bar).Turn the control knob to the 'Reset' position for five seconds and then back to the 'On' position.
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A boiler cover plan would cover faults like D — 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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