CH gone on lower floor. Any suggestions??

The usual system is that the programmer/time switch feeds the thermostat which, in turn, feeds the zone valve. If the zone valve isn't opening, it could be due to one of several reasons:

• duff zone valve
• duff thermostat
• no feed from programmer to stat
• duff wiring berween stat and zone valve

The fact that the stat doesn't click when you move it past the actual temperature of the room it's in (I think that's what you're saying?) means that the stat is the prime suspect. If you feel comfortable doing so, short out the two wires going to the stat ** and see whether the zone valve then opens. If it does, it's definitely the stat.

Roger

Many thermostats will click regardless if they have power to them or not

- assuming you can 'rock' them either side of the actual room temperature.

Have you tried moving the arm on the valve by hand? That's what it's there for - to operate it if the electrics fail.

If this works, then either the thermostat, valve, or the power to them has failed. If you know a half decent electrician, I'd get him to look at it rather than a plumber - central heating systems often have the most appalling standards of wiring installation.

Thanks for the advice Roger. I've taken the thermostat cover off - I will try this tomorrow (during the daylight). I just want to confirm one thing :

there are 3 wires going into the thermostat base (unfortunately all brown).

However on the thermostat base moulding where the 3 wires go in, the moulding is labelled 'N', 'L' and '3' . Your last comment made me wary of going ahead before I get a reply. Can you just confirm that I should connect a shorting wire between the N and L wires. (I'm assuming the wire which is marked '3' on the thermostat is the earth....).

Thanks

This 'stat sound like a mains fed one, so you shouldn't (Should Not) short over L and N. The 'stat is more likely to be a switched live which controls other mains fed appliances in the system.

Is it an electronic thermostat ? Does it show numbers on a little screen ? Does it have a light inside ?

No comment. ;-)

Seems very analogue to me. No lights, no display, just a plastic rotary dial on the front... going to keep on waiting a bit :)

Dave- firstly, the working thermostat (upstairs) does not click when the heating is not on.

Secondly, I'll try moving the valve by hand when I get back tonight. Thing is, that still won't tell me whether it's a broken thermostat or a broken valve actuator (motor) or loss of power will it.. I think I need someone with a multimeter... or buy one.

No, DON'T short L & N - you'll get a big bang! Try to work out which wires are connected to the contacts - almost certainly L & 3.

Roger

Right - older basic mechanical ones do as you're just hearing the contacts mating. Dunno about new basic ones - I've got a programmable one which is battery operated and gives a vast clunk when it operates. ;-)

If I had to guess, I'd go for the motorised valve as thermostats rarely fail.