BoilerFaultCodesYour boiler is not broken; it has simply noticed the cold weather and is running automatically 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: Boiler frost protection - boiler will fire if temperature is below 5ºC.
What causes this fault?
This status appears when the boiler's internal sensor detects that the water temperature has dropped to a level where there is a risk of freezing. It triggers a safety sequence that fires the burner to gently warm the system back up to a safe operating temperature. This is a normal protective function rather than a mechanical failure.
This code is exclusively seen during the winter months or during sudden overnight cold snaps when external temperatures drop below 5ºC.
DIY fix possible
No action required - the boiler is working as intended.Ensure radiators are turned on so water can circulate during the frost protection cycle.Check that the condensate pipe outside is not frozen if temperatures are extremely low.
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 F — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.