Newish boiler but old wiring to thermostat

TornAtTheShoulder

Hi. I had a new combi boiler installed about 7 years ago and the installer said he would wire it to the existing room thermostat. Well, the thermostat has never worked, ie no matter where it's set the boiler just keeps running. FINALLY, i decided to have a look at it and removed the face from the thermostat. The wiring inside is the old kind (red and black) with 2 thinner brown wires. Surely if the installer had connected the boiler to the thermostat it would be blue and brown wires??? Did he just not do it after all? I have photos but don't know if or how to insert them.

Thanks for any help. :huh::huh:

Myser

Firstly, upload your photos to a file sharing site such as TinyPic:

http://tinypic.com/

Select the message board size when you upload. You will be given a link for your photo.

Reply to this thread in Advanced mode. Click the landscape icon (picture of a mountain on a yellow background).

Insert the link from the photo sharing site in the box that pops up. Repeat for multiple photos.

TornAtTheShoulder

Myser

You would need to look at the boiler wiring. If the link for the external thermostat hasn't been removed, then it will have no effect.

Do you have Thermostatic Radiator Valves on all but one radiators in the house?

TornAtTheShoulder

Would he have simply twisted the wires from the boiler with the wires from the thermostat, rather than running the wires from the boiler directly to the thermostat terminals, ie he has connected the old and new wiring somewhere along the run of wiring?

Only one radiator has a TRV.

ValHaller

Couple of points

• As Myser indicates, there may be an issue at the boiler end. The fact that the cable at the thermostat end is old does not mean that your installer did nothing - it could well be wired in at the boiler end, but with a short circuit across the switch contact
• Mains thermostats of this age should normally be wired with 3 core + E cable. They need a neutral connection for the anticipator heater, otherwise they tend to have too wide a band between hot enough to switch off and cold enough to switch on

Myser

TornAtTheShoulder wrote: »

Would he have simply twisted the wires from the boiler with the wires from the thermostat, rather than running the wires from the boiler directly to the thermostat terminals, ie he has connected the old and new wiring somewhere along the run of wiring?

Only one radiator has a TRV.

As ValHaller said, there is nothing wrong with reusing the older red and black wire. What you need to establish is whether the connections from the thermostat have continuity back to the boiler.

If you are competent with electrics and own a multimeter, you should be able to do this easily.

Sometimes, when new boilers are installed, the thermostat may be omitted if all but one radiators have a TRV fitted - hence why I asked. This isn't good practice though.

TornAtTheShoulder

Thank you Myser and ValHaller. No, I'm not particularly competent with electronics and I don't own a multimeter. But you have answered my question! I know now that the old wiring doesn't mean that there was no attempt made to connect the two. Although . . . What are the two thinner brown wires? One of them goes nowhere?

Myser

They may be earth wires but it's difficult to tell from the photo.

TornAtTheShoulder

Thank you. Another question! Why are the black wires terminated at the screw? I've looked at wiring instructions for this unit and it's not like that!

Myser

TornAtTheShoulder wrote: »

Thank you. Another question! Why are the black wires terminated at the screw? I've looked at wiring instructions for this unit and it's not like that!

I only see one black wire?

Which wiring instructions/diagram are you referring to?

The model of your thermostat would be useful.