Central Heating problem

[Springy]

We may have a bit of an emergency, i.e. we have turned on the central heating for the first time this year, the radiators started to get hot but now have cooled. I can here the wall thermostat "click" when I turn the temp. up, but the boiler does not fire up. The timer is switched on to "constant".

Using my fabulous and, let's face it, legendary diagnostic skills I have turned up the 'stat strapped to the HW tank, and that fires up the boiler, so, I think, the boiler/pump etc. are ok (thank heavens).

My thoughts are that even though I can hear the heating 'stat click when I turn it up I don't think it is closing the connection that tells the little green wizard to turn the boiler on, i.e. I may need a new heater 'stat.

Am I close? any way I can prove this, e.g. is it safe for me to take the cover off the stat and short out the contacts? Does mains appear at the 'stat, or is it a nice safe 5 volts or so?

Any help, etc.,

Neil. X X X.

[John]

The boiler might not respond immediately if it already has some heated water in the heat exchanger - but soon will when the pump moves it.

[John Rumm]

Firstly the stat is quite likely to have mains on it - so take care.

You have not really told us enough about your system to give you an exact answer, but your problem does sound like a fairly common one to affect some categories of system that have a three port valve of some sort. This directs the flow of boiler heated water to either the cylinder or the rads, or with some systems with the right type of "mid position" valve - both at once.

are your valve has stuck over the summer through lack of use. It is quite common for the call for heat from the room stat to go to the valve and not the boiler directly. There is a microswitch on the valve that in turn closes when the valve moves to the heating position that should fire the boiler. If the valve does not move - no heat.

See:

valves can be a result of a stiff mechanism (i.e. the wet bit), or a failed motor. You can usually take the motor off and check you can move the valve itself with pliers - if it is stiff or siezed, there is your answer. Moving it manually may free it and fix the problem. If it turns ok, then you may need a new motor (readily available and easy to fit).

[Springy]

Thanks guys, there is a picture of the valve in virginmedia.test, the slider has three positions, w, m, h. It is in the m position and I cannot move it. I'll have a dismantle tonight and let you know.

TX again,

Neil.

[Geo]

Virginmedia groups are only accessible to VM customers so you should post the picture somewhere else for everyone to see it.

Geo