BoilerFaultCodesWhat the manual says
Manufacturer manualFrost protection mode
What causes this fault?
This occurs when the internal temperature sensors detect that the water inside the unit has dropped below a safe threshold. To prevent the heat exchanger from cracking due to ice expansion, the boiler automatically starts the pump or burner to circulate warm water. It is a safety feature rather than a component failure, triggered purely by the ambient or water temperature falling too low.
This code is almost exclusively seen during winter or unexpected cold snaps when temperatures drop toward freezing.
DIY fix possible
Check that your external condensate pipe is not frozenEnsure radiators in cold rooms are turned on slightly to allow water circulationWait for the temperature to rise, as the code will disappear once the water reaches a safe temperature
Avoid the next call-out bill
A cover plan would handle faults like S.34: no call-out fees, no surprise bills.
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