Frost protection

1 What it does

The function checks the temperature inside the boiler and acts if it falls too low. Baxi's quick start guide warns that a boiler may run for a short time in cold weather with the heating off, for this reason³. Ideal's Logic+ guide lists boiler frost protection as a normal operating state, not a fault⁶. Figures differ, so do not assume yours matches another maker's.

2 Its limits

Vaillant says plainly that the boiler alone cannot ensure the whole installation is protected and that a separate thermostat may be needed². Baxi's 600 Heat guide says a frost thermostat can protect radiators in rooms at risk, such as a garage⁵. Viessmann's manual also separates protection of the boiler from the rest of the system¹⁰. Fitting one is a job for the installer.

Power is the other limit. Worcester Bosch's 24/28 manual says not to turn the boiler off, as that deactivates frost protection¹. Its Greenstar 4000 manual warns the system can freeze during a power failure or boiler fault¹¹. Vaillant's 2023 manual says the standby button keeps protection active, while switching off at the fused spur does not⁴. Glow-worm's Energy7 standby mode also keeps it active¹².

The function does not thaw a blocked outside drain. For that, see frozen condensate pipe.

3 If the house will be empty

Manuals differ, and they are not interchangeable.

For a longer absence, or if heating cannot be kept running, Vaillant says to have a competent person drain the system¹³, and Baxi says your installer can advise⁵. Do not drain it yourself. Rooms you use still need warmth; see the room thermostat entry for official temperature advice. Before winter, Baxi suggests testing the heating and lagging exposed outdoor pipes¹⁴. Oil boilers were not checked for this entry.