BoilerFaultCodesYour boiler has likely stopped because it detects it is getting too hot too quickly, often caused by air trapped in the system or a blockage preventing water from flowing properly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Boiler operating at higher flow temperature / Air passing through the pump (if shut down occurred)
What causes this fault?
This fault occurs when water is unable to move through the boiler quickly enough to carry heat away from the burner, leading to a sudden temperature spike. The most common reason is air trapped inside the internal pump or a physical blockage in the pipework that is restricting the flow of water. If the pump has failed or is struggling to push water, the boiler will shut down as a safety precaution to prevent internal damage.
This issue often appears in autumn when the heating is turned back on for the first time, as pump components can seize or air can settle during the summer months.
DIY fix possible
Check that your radiator valves are fully openBleed your radiators to remove any trapped airCheck the system pressure gauge and top up to 1.5 bar if it is lowRestart the boiler using the reset button
Find a Gas Safe engineer
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A boiler cover plan would cover faults like 2 — no call-out fees, no surprises.
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Potterton Envoy 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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