BoilerFaultCodesYour boiler has detected very cold temperatures and has automatically turned itself on 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: Anti-frost mode is active
What causes this fault?
The boiler's internal temperature sensors have detected that the water inside the unit has dropped below a safe threshold, typically around 5°C. To protect itself from damage caused by ice expansion, the boiler automatically fires up to circulate warm water until it reaches a safer temperature. This is a built-in safety feature rather than a mechanical failure.
This status code is most common during the winter months or during overnight cold snaps when external temperatures drop significantly.
DIY fix possible
Check that your external condensate pipe is not frozenEnsure your thermostat is set to your desired temperatureWait for the boiler to finish its warming cycle and return to normal operation
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 S.34 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.