Room Stat not shutting off heating

[Golfer1]

Hi there,

I have the following problem:

- Both CH and HW work fine. Boiler fires and timer works correctly.
- But for CH, the room stat does not close off boiler, even when turned right down

I have done some investigation. The room stat has L, N, E and Call connections. When I test the L connection, there is no power. This, I assume, is not correct. My assumption = no power to stat therefore no control and the boiler just keeps firing.

As there is no live supply to the room stat, it's reasonable to assume that the stat itself is fine. It's the thing feeding it.

This leads me onto my question, Where does the stat get its live feed from? There is a fused spur next to the boiler with a myriad of wires running from it ("Load" connections). Does the room stat feed from that (usually), or is it fed via the timer switch somehow? I'm guessing the problem lies with either my timer switch (if that is involved at all) or the boiler control circuit board itself, or the fused spur.

Any ideas?

I'm going to get an engineer out but wanted to rule out anything obvious first.

If it makes any difference, I moved into the house 2 months ago. The fused spur was replaced (like for like) as it was damaged. Could the spur have been wired wrongly? It has a single set of wires into the SUPPLY (L, N and earth) and then various L,N and E coming out of the LOAD. Curiously there are three of everything coming out of the fused spur LOAD, except for LIVE where there are only two wires coming out. Strikes me as odd.

Sorry if I am not maing much sense - just thought I'd ask in case it was obvious.

Thanks as always,

Ed

 

[ollski]

2 x 2 port zone valves in airing cupboard?, sounds like heating one stuck on.

 

[Golfer1]

Would that explain the lack of live power to the stat?

 

[nickso]

yes.

 

[Golfer1]

OK - I've got the 2 valves in the cupboard - each one with a little lever on it (on / off I guess). How can I test the theory?

Sorry to be dim - but it sounds like something I can try myself!

Not a plumber you see...

Ed

 

[Golfer1]

Not sure it's the valve. As the CH is switched on and off it moves from one position to the other making a motorised "whir". I think that's what it is supposed to do...

 

[nickso]

and the hot water one?

 

[Golfer1]

Hmm - the HW one does not seem to move - seems to stay in the same place. But the water heats up OK (so must be "on"). Should it move too and fro as the water is switched on and off?

 

[nickso]

its possible then that its stuck in the on position.

there is usually a slot in the valve body that indicates the valve position....sometimes has a-b written next to it.

turning the hot water stat up and down should make the valve open and close.

 

[ollski]

You are going to struggle to indentify the problem without a mulimeter to see which valve is feeding power. You could isolate power, remove one of the two orange wires in the wiring centre and reintroduce the power with nothing calling for heat. the orange wire that still fires everything up while connected is leading to your faulty actuator.

 

[Golfer1]

I have a bit of an update. Perhaps this will make things clearer.

I noticed last night that when the room stat is in place (wired in), the boiler fires the heating all the time. Regardless of whether the room stat is at 10 degrees or 30.

However, if I take the room stat off the wall (disconnect it) the CH does then switch off.

So, this would imply to me that the “signal” from the stat is being “understood” by the system afterall – correct? I am mimicking the on-off routine by putting it on the wall / taking it off.

So, this would suggest to me that the stat is faulty.

I also noticed that the analogue stat doesn’t make a click when it reaches room temp (as they usually do). This again suggests to me that the internal switch is not working. In my experience, these analogue stats always make a click as they reach room temp. This one doesn’t which again makes me think it’s duff.

Is my analysis sensible or am I being a plank?

Thanks so much for your advice – if I can simply replace the stat that will save me a call out charge. I’ll buy you a “virtual” pint!

Ed

 

[ollski]

I thought there was no power at all to the room stat....on any terminal?

 

[Golfer1]

To test for power on the stat terminals, I used one of those electricians screwdrivers – the ones with the neon bulb in the handle. That did not light on any of the terminals. The driver works fine as I tested it on a light switch and it lit up as usual. So, from that I assumed no power.

However, the fact that removing the stat switches off the boiler would suggest that my assumption is wrong.