Room Thermostat Not Working - Help Please!!

My room thermostat does not appear to be working , i.e it is not cuttin

off the heating when it reaches its temperature, therefore the heatin is just constantly belting out heat, I have took the casing off an cleaned it out in case it was the connection but no difference. Ca anyone advise what else I should do or do you think it needs replacing Cheer

-- Daz G

Reply to
Daz G
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Hi

First I would check the thermostat electrically. With the usual provisos of "be careful, it's probably got 240V across it, don't do this if you are not confident of your competence etc":

Stick a multimeter set for an AC range > 250V across the contacts with the system powered. Twiddle the knob until you hear the click.

Either side of the click, you may read 0V and 240V - if so, thermostat is OK.

If 240V, twiddle again until it goes click and you should get a reading of

0V.

If it always reads 240V irrespective of contact position, then the contacts are probably knackered or some other open circuit fault.

Used this method last week to prove my Dad's HW thermostat - transpired the

2 port valve was seized. I proceeded with extreme care as the "professionally" installed wiring was a fecking rat's nest of crap stuffed into a junction box, in fact to call it so is disrespectful to rats. Had to remake one connection for being half out of the (one of many) bits of choc block. Why can't the cheap gits use a proper terminal box? Labelling would be nice too. As would strain relief. And they wanted to ban DIY electrics. I ask you. Wasn't dangerous when I'd fixed it, to be honest it wasn't particularly dangerous before, but it was still a disgrace.

Sorry - back on point:

If it always reads 0V, then either the contacts are stuck (or some other short circuit) or your have a DC control signal to the boiler (how likely I don't know - all the boilers I have experience with present mains at the room thermostat). Or you have a very low AC voltage and your meter isn;t sensitive enough. A digital meter should be fine though.

You should probably at this point remove the thermostat from the circuit after proving the boiler supply is isolated and the thermostat has no stray live voltages in it (no accounting for previous wiring and possible multiple live feeds to different parts of the heating controls).

Then test with the meter on a low resistance range following the same procedure.

If your brave and you know your meter will stand it, you *could* test in situ on a DC range of about 400V (to allow for mains peaks if you were wrong). In this case, I'd have a good probe around on the >250V AC setting to known earths/neutrals to convince myself that there really wasn't mains present.

This is USENET - if you don't feel comfortable with the above, don't do it :)

HTH

Tim

Reply to
Tim S

Ah, diybanter. If your stat is managing to switch the 240v, its something else, most likely the 2 or 3 port valve. If your stat doesnt switch the 240v, the stat aint right.

Stats have 2 3 or 4 wires.

2: live, switched live 3: as above plus neutral to power the compensation resistor 4: as above plus earth

If you dont know how to do it safely, dont, as it will be live while testing.

If its a bimetal stat, as it probably is, and it isnt switching, stuck contacts can be wiggled apart and the surfaces smoothed with a rats tail file or very fine sandpaper. Obviously dont do this with power connected to it.

Doing this could knock the alignment off, so afterwards slowly turn it till it clicks, to see if air temp matches dial temp. If not, adjust.

NT

Reply to
meow2222

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