BoilerFaultCodesYour boiler has detected very cold temperatures and is circulating water to prevent the internal pipes from freezing.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: Pump Overrun - Used in Frost Protection
What causes this fault?
This code appears when the boiler's internal sensors detect that the temperature of the water inside the unit has dropped below a safe level, usually around 7°C. To prevent the heat exchanger from freezing and cracking, the boiler automatically switches on the pump to move water through the system. This is a built-in safety feature rather than a mechanical failure.
This status code is almost exclusively seen during the winter months when external temperatures drop near or below freezing.
DIY fix possible
No action is required as this is a normal safety function.Ensure your thermostat is turned up if you want the heating to stay on.Check that any external condensate pipes are not frozen if the weather is extremely cold.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like b — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Potterton Envoy Plus 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.
Affiliate links — we may earn a commission at no extra cost to you.