Central Heating starting up during the night

[kch]

Hi,

I have a problem where my central heating is starting up during the night (but not during the day, as far as I know), and all radiators are getting warm. Last night it was from around 3:45am to 4:05am. Our set-up:

Potterton Suprima conventional boiler approx 8 years old, serviced yearly

Megaflow style hot water tank, 15 months old

Honeywell thermostat

Hot water and central heating control valves (Honeywell) replaced earlier this year

(all the above is in the loft)

Control panel in kitchen, currently set to so that water is heated in the morning and late afternoon, central heating is set OFF

I did get up last night and check that the hot water and central heating were both off, but I coudn't go up into the loft to check the valves/switches and the boiler itself. I tried switching the hot water and cnetral heating on then off, but this made no difference

Any ideas what this could be ? Coudl the thermostat be way off and think that the loft is cold enough to fire the boiler/central heating ? I would imagine that the TRVs are currently set so that the radiators shouldn't be coming on anyway, but the ones I touched were definitely hot.

Thanks,
kch

 

[GrahamM]

First thing that came to mind. Colder nights and 'Frost thermostat'.
Not much experience of them, but as the boiler is in the loft they are sometimes fitted to protect the heating system freezing.
Could you have one that needs adjusted?

 

[kch]

I can only remember it coming on in the depths of winter - end of August does seem a bit early! As for adjustment, I don't remember seeing any external controls - do I need to take a cover off and adjust it internally somehow ?

Thanks,
Keith.

 

[GrahamM]

I know here in sunny scotland the temps have plummeted past few nights.

A frost stat usually looks like a normal room stat without the dial control. Should be somewhere in loft. If set up correctly they will bypass all other controls.
It has no external control to stop people messing around with it, as if set up incorrectly you could be in for a few pounds worth of repair bills if the system was to freeze. They can be adjusted however internally, but only attempt this if you are confident of what you are doing.

Some boilers have a frost stat built in.

 

[kch]

Thanks for the responses.

We definitely have a Honeywell frost thermostat - I have seen it on the wall above the boiler. I live in Berkshire, and the internal temperature (in the upstairs bedrooms anyway) has not fallen much below 20 degrees C.

I had a look in the loft last night, and we have a Honeywell Frostat. Anyone know how easier/hard they are to adjust ? Or should I replace ? Or bypass completely until the winter ;-> ??

The central heating kicked in again last night, around 4am...

 

[Rox]

The Honeywell T4360 frost stat can be adjusted from 0 to 20 deg C (according to the literature), but is supplied preset at 5 deg. and I'd be surprised if your installer changed that. I've not seen inside one to know how you adjust it - sorry.

You don't say which timer model you have. Central heating systems can come on earlier than expected if you have one of the latest Honeywell timers/programmers which have an "Optimum Start" option. If this option is selected, the programmed "on" time is not the "boiler on" time, but the time when you want the house to reach the preset temperature. The controller "learns" how long it takes for the home to heat up and monitors the prevailing temperature daily, then delays boiler firing until the latest time when the set temperature can be achieved by the required time that day. So the boiler fires earlier than expected, if you've enabled the feature.

But as I doubt you're using your central heating yet, the frost stat sounds the likely cause.

 

[kch]

Thans Rox.

Nope, we don't have one of them fancy timers which come on early so that the time you set is the time you want to be up to temperature (we had one of those whilst living in the States last year and it confused the hell out of me).

I iwll open up the frost stat tonight and have a look - if it is still set at its preset value (5 -> 7 degrees), then it looks like I will need a new one...

 

[ferret]

Thans Rox.

Nope, we don't have one of them fancy timers which come on early so that the time you set is the time you want to be up to temperature (we had one of those whilst living in the States last year and it confused the hell out of me).

I iwll open up the frost stat tonight and have a look - if it is still set at its preset value (5 -> 7 degrees), then it looks like I will need a new one...

You should also have a return pipestat fitted in conjuction with the frost stat , you should find it strapped to the boiler return and set at about 40c this is to ensure that the rads dont get too hot and trhe boiler is on for the minimal time

 

[kch]

Mystery solved - I now have a (broken) Honeywell FrostStat T4360A sat next to me. When I took of the case, I moved the dial around and it was cliking on and off at around 10 degrees C, when in fact the temperature in the loft was around 27. I then noticed that one of the posts which keep the dial in place had sheared, so the button behind the dial was being depressed at too low a temperature on the dial.

Thanks for all the input.