Frost thermostat ?

[DaveHerns]

My mother has her CH boiler in an outside toilet and there's a thermostat by the boiler set at 3 degrees . I asuume this fires the boiler if the temperature drops that far but would it be wired to fire the boiler if the timer wasn't set to be on ? Otherwise if it isn't "independent" from the programmer I can see a situation where it doesn't give the protection expected .Does it just run the boiler long enough to raise the temperature of the water a few degrees and cycle on and off ?
I've just put her heating on 24 hours for this cold spell to be safe

 

[TCCHeating]

If the frost thermostat is wired correctly. It should run the boiler independantly of the programmer.

Most frost thermostats are wired to just run the boiler until the frost thermostat is satisfied. (Ie the tempreature of the area in which the frost thermostat is located raises above 3 degrees). This could mean that the boiler could fire for a long time. Depending on the position of the frost thermostat.

However, there is a much better way to wire them. A good system will have a frost thermostat wired in conjunction with a pipe thermostat. (Connected on the return pipe to the boiler). Using this method less energy is wasted as the frost thermostat only fires the boiler if the pipe thermostat is not satisfied.

 

[DaveHerns]

Thanks . Now I understand the theory . I'll probably leave it as it is as it's never frozen up yet and that's my big concern rather than saving gas . I will tell her to shut the window though !

 

[DaveHerns]

Looking at the installation again today I see it has a thermostat fixed on the wall near the boiler set at 3 degrees plus (what I'd missed) a pipe thermostat set at 22 degrees . Is this correct? If so British Gas did a good but expensive job!

 

[TCCHeating]

Yep. Sounds good to me