Theben Ram 701 Room Thermostat

[Philpee]

Please can anyone help me? I am replacing an old Honeywell Room Thermostat (no model number on it) with the Theben 701. I have three wires in the old stat, red, black and earth. Reading the posts, I suspect the earth may not be an earth wire.

Can anyone tell me where the wires should go in the Theben? I have four terminal connectors numbered 2, 1 N and N. I have tried to make sense of it and researched as far as I can, but cannot find an answer.

Thanks for any help

 

[stem]

For the Theben, the 'N' terminals are both neutrals. (two terminals are provided to use as a link if two cables are used) '1' is the live supply, and '2' is the live return or switched live. There's an installation leaflet here that explains (see diagram 10 for wiring info) I would have expected that one should have been included with the thermostat.

It's not possible to say which wire is what, it all depends upon what the installer connected them to at the other end. However, with a few more clues we should be able to figure it out. Why do you think the Honeywell earth wire is suspect? What terminals on the Honeywell are the wires presently connected to?

 

[Philpee]

Hi Stem,

Thanks for replying. The Honeywell has four terminals, numbered 1-4. It is wired:
1=Black
2=red and
4=green.

I thought that the earth wire may not be used as an earth wire, but may be used as something else (just from what I read on this forum elsewhere).

I thought this would just be an easy switchover for a layman while I was decorating!!

 

[stem]

Hmm. Could really do with the thermostat model to be sure. Have you looked inside the cover? Failing that is there a wiring diagram inside the cover? If so could you photograph it?

Older thermostats usually needed three wires a 'L' 'N' & 'Switched L' so you might be right about the earth.

 

[Philpee]

Here are the pics
//media.diynot.com/18000_17731_21371_74993859_thumb.jpg
//media.diynot.com/18000_17731_21370_57682350_thumb.jpg

 

[flameport]

Wiring diagram

• Philpee
• 7 Apr 2010
• 2

The old thermostat has been wired using the CPC as the switched live. Also appears L and N are reversed (or the cable colours are reversed)

You cannot connect the new thermostat to the old wiring. The cable needs to be replaced with 3 core and earth.

The only other solution is to reconfigure the existing cable for live, switched live and earth, and then fit a thermostat which doesn't need a neutral connection.

 

[bongos]

Can't make out what's going on in the second pic. Any chance of a larger one? Can you trace the cable back to the wiring centre at your boiler?

If the earth core has been used as a live conductor and you require live/switched live/neutral for it to work then you must replace the section of cable with 3c+e. Either way the earth must be an earth!

EDIT: Too slow.

 

[stem]

Thanks for the photos. Flameport & Bongos are right, and as you suspected, the earth is being used for the 'switched live'. Old style mechanical thermostats need 3 wires because they have a neutral to operate a little heater called an accelerator. This helps improve the accuracy of the mechanics. Newer digital thermostats are more accurate than the mechanical bi-metallic type you already have (& which the Theben also is) and don't need the heater, so only 2 wires are required, therefore, you could fit one of these without too much difficulty, although the wires at the other end would need swaping over to sort the earth problem out. Here's an example of a 2 wire thermostat.

Untitled

• stem
• 2 Feb 2010
• 4

If you do get one, post again if you need any help installing it and changing the wiring over at the other end of the cable.