central heating on even though not timed to be

[littlesaur]

My central heating came on in the middle of the night even though it was not timed to be on. When I checked the timer, the timer was not on. The timer came on as usual at 6am and turned off as usual but the heating is still on although I don't think the water is (the motorised valve is shut) The timer is a Honeywell ST6400 and was only fitted 3 weeks ago in an attempt to remedy an ongoing problem with the heating and hot water not always coming on in the morning. I have also had a new motorised valve for the water.

 

[ollski]

do you have a frost stat near your header tanks?

 

[littlesaur]

That could be it..The boiler is in the garage and there is a thermostat next to it - at least I think it is a thermostat - identical to the one in the hall but no temperature markings. The cold water tank is in the loft/rafters above the garage.

However, could this be connected with the intermittent problem we have been having with the heating not coming on in the mornings?

The boiler is an Ideal Minimiser SE.

Thanks

 

[ollski]

The frost stat will override everything and fire your boiler up when the temperature nears freezing usually middle of the night.
Minimiser needs an annual service wich includes a clean out of the combustion chamber otherwise condensation will prevent it firing in the mornings.

 

[littlesaur]

Thanks for all your help.

We had the boiler serviced in November and everything was fine for 6 weeks and then it started not coming on in the mornings once or twice a week. Is there anything I can do to stop condensation?


The whole system is less than 3 years old.

Reading through the forum I had thought of the frost stat but it had never come on before.

Thanks again

 

[COG]

your external frost stat should be wired into a pipe stat set at say 30 deg c at the return to the boiler,that way the frost stat will fire the boiler to protect it from frost and the pipe stat will shut it off once the chill is taken out of the htg system on its own it wont switch off untill the garage heats up or the outside temp drops.