BoilerFaultCodesYour boiler has switched itself off because it has become too hot internally, likely due to a lack of water or a blockage preventing water from moving around the system.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Over temp. lock-out or circulation failure. Check pump, 3-way valve & CH water pressure. Replenish system & purge air/water via manual vent
What causes this fault?
This fault occurs when the water inside the heat exchanger reaches a dangerously high temperature, triggering a safety shutdown to prevent damage. The most common reasons are a pump that has failed to move water around the system or a blockage in the pipework that is trapping heat inside the boiler.
This fault often appears during the first cold spell of autumn when the heating is turned on after a long summer break, which can cause internal pump components to seize.
DIY fix possible
Check the pressure gauge on the front of the boiler; if it is below 1 bar, top up the system using the filling loopEnsure all radiator valves are open to allow water to circulateBleed all radiators to remove trapped air and then top up the pressure againCarry out a manual reset of the boiler using the control knob
Find a Gas Safe engineer
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A boiler cover plan would cover faults like A03 — no call-out fees, no surprises.
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Potterton Powermax HE is discontinued — time for a new one?
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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