Simple Question

[ragj195]

Hi

I removed a very old room thermostat and puchased a new one. Can someone please tell me how it should be wired as the instrucitons don't seem to make sense, maybe the wiring is old or something. Coming out of the hole in the wall is 3 core cable with an earth, a black and a red wire.

Will the heating work if I don't reconnect a new thermostat straight away and if so what do I do with the wires, join the red and black or leave them disconnected?

Basically what the hell do they do and do I need a certain type of thermostat to suit the wiring?

Thx

 

[Slugbabydotcom]

Dont count on that earth wire being an earth wire !!!
It could be a neutral with the other two being a live and switched live.
Don't recommend you play with it unless you at least have a clue.

 

[Softus]

<slight cock-up - I managed to edit my own post instead of adding a new one - too early in the morning obviously>

 

[ragj195]

The system is an open vented gravity system with a very old Concord WRS boiler. The old thermostat is long gone now and I took the new one back to the shop yesterday so still to buy one. I wish I kept a record of the wiring on the old one now!
I may have done a stupid thing but I connected the black and red wires and it didn't blow anything. There seems to be a low voltage on them. Where do the wires trace back to? Will it help if I check that?

 

[chrishutt]

Where do the wires trace back to? Will it help if I check that?

Yes, you should have done that first of all. The wires will run back to either the boiler, the programmer but most likely a junction box (white, rectangular or square, two screws on cover).

Switch off electricity and open this and make a diagram of the wiring connections withing, identifying as far as possible what each cable connects to (e.g. boiler, pump, etc).

 

[Softus]

<Oh b*m, now I've overlapped with chrishutt's post; I'll post this anyway and leave you to decide whose questions to answer - sorry>

Don't fret, I expect we can sort this out.

If I remember correctly your boiler has a simple programmer built into it. It's very likely that it uses a three-wire roomstat connection. If you could describe your old roomstat then I (or others here) will probably work out what it was.

If you're competent with electricity, then carefully measure the voltages at the three permutations of wire pairs at the roomstat end, and post the result here.

Also, please tell us the colour of the wires at the roomstat end.

If things go as I expect, you should be able to buy a simple replacement, e.g. Honeywell T6360, but please give the above information first.

 

[ragj195]

Okay thanks

The wires at the room stat end are earth, black and red. There is a white junction box by the tank so I'll take a look at that. The old stat was very old looking. As far as I can remember it was similar in size to the simple newer ones but beige with a circular dial and what from the outside looked something like air vents running across the bottom panel that faced down.

 

[Softus]

Have you measured the voltages on those three wires?

 

[ragj195]

I'll do that this morning. What I do know is that when you join the black and red they spark a little but if you turn the boiler to the OFF position it doesn't. That must sound so bad but I just happened to find that out.

 

[chrishutt]

when you join the black and red they spark a little

Do you know what you're doing? That could well be mains voltage!

The chances are that the red is the switched live from the programmer (CH on) and the black is the switched live back to the pump (and boiler). the "earth" wire is probably a neutral connection to allow the room stat accelerator to work.

 

[Softus]

You have this one covered chrishutt, so I'll leave you to it! You might want to keep a defibrillator within reach though

 

[ragj195]

no shocks yet! Voltmeter says 240 so I guess that would be mains voltage then! My problem is that the boiler keeps cutting out. I thought it was the pump so I changed that this morning. The new one is whirring away now, all the pipes around it are very hot but the rads are still cold which is as it was before. I've drained and filled the system and ran it through to clear any air from it also.

I'm now pretty sure it all co-incided with me removing the 70 year old room thermostat!

One other thing about the pump. I double checked the direction of flow indicator on the old pump and it was pointing down with the label the right way up. I made sure the new pump also had the arrow pointing down even though this meant the fron label is now upside down! Is this normal?

I'm starting to give in, the wife is shouting at me and the newborn baby is crying coz she's so cold. Don't you just love weekends ;-(

 

[ragj195]

It's all working! Was definitely the pump but the thermo just made things even more confusing. Anway if I turn the stat down the pump cuts out and up again turns it on so all seems well (I think).

Thanks, you guys!!