BoilerFaultCodesTechnical description
The frost thermostat calls for heat (contact closed) and overrides the Celcia 20 control, causing the boiler to operate continuously to achieve the flow set point.
What causes this fault?
This fault occurs when an external frost protection device becomes stuck in the 'on' position, sending a constant signal to the boiler. The boiler believes the pipes are at risk of freezing, so it continues to burn fuel and heat the water regardless of what your thermostat is telling it to do. This is usually caused by a faulty frost thermostat sensor or a short circuit in the wiring connecting that sensor to the main control board.
This fault is most common during late autumn and winter when temperatures drop, as this is when the frost protection system is actively cycling on and off.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.