Replacing a room thermostat - mechanical to digital

[mikefromguildford]

Hi. Want to replace my Drayton (RTS1) with a good digital one. I've attached my current wiring setup. Could anyone suggest a good digital room thermostat that I (a wiring novice) could install? Many thanks. Mike

Untitled

• mikefromguildford
• 30 Oct 2012
• 1

 

[OwainDIYer]

Many modern digital programmers are battery powered, so provided they can switch mains (most can) connect the C and NO switch contacts to Red and Yellow, insulated and make safe Blue and Grn/Ylw.

 

[Agile]

That would only be good advice if they have been wired according to the expectation.

Commercially we cannot assume anything and I would always test before connecting a new thermostat. I cannot afford to damage a new thermostat by making assumptions!

Tony

 

[mikefromguildford]

Thanks. Is there anything I can do myself to ascertain what's what? Any suggested thermostats that I could look into? Many thanks

 

[Agile]

You dont say what boiler but regardless ANY thermostat which will give volt free contacts rated at 230v will suit.

Most now are battery operated so dont need a neutral connection.

Tony

 

[mikefromguildford]

Thanks Tony
It's a Vaillant ecoTEC Plus 418 Open Vent btw

Don't mean for you to draw me a picture but would you therefore expect a Honeywell DT90E or similar to work?

http://www.plumbnation.co.uk/site/honeywell-dt90e-wired-digital-room-thermostat/

Thanks

 

[OwainDIYer]

Yes. Red is to A and yellow to B.

Terminate and make safe blue and green/yellow.

 

[D_Hailsham]

You don't say what boiler but regardless ANY thermostat which will give volt free contacts rated at 230v will suit.

Wake up Tony!

The OP doesn't need to tell you what boiler he has! He has already told you that he has a RTS1 thermostat which, as you should know, is a 230V only stat. A quick check of the manufacturer's wiring diagram would also tell you that the wires are correctly connected: Blue to N; Red to L; Yellow to terminal 3, the switched live.

The Honeywell DT90E will do perfectly.

Connect Red to terminal A
Yellow to terminal B
Make the Blue and Green/Yellow safe; e.g stick them in separate holes of a small terminal block.

Terminal C is not used.

 

[doitall]

Or the op could even use the Honeywell DT92E and put the receiver where the old stat is.

View media item 51960

 

[mikefromguildford]

Thanks all. Sounds like it's worth giving it a go myself. Much appreciated. Mike

 

[mikefromguildford]

Sweet. DT90E purchased, installed, and is working. Easy when you know how! Thanks all

 

[Charnwood]

On a similar vein, I'm wanting to replace a Honeywell T6360B1028 with a CM907. Is this feasible? If so, what's what with the wiring?

Currently (6360) terminals 1, 2 and 3 are brown, blue and green/yellow respectively.
The wiring diagram for the CM907 shows 2 terminals in use.

I presume earth (green/yellow) needs isolating, but which wire goes to terminal A, which to terminal B in the 907?

 

[OwainDIYer]

Currently (6360) terminals 1, 2 and 3 are brown, blue and green/yellow respectively.

If that's the case that is seriously wrong. 1 is Live, 2 is Neutral, 3 is NO (normally open) (switched live call for heat).

Using green/yellow for any purpose other than earth is very wrong.

The existing wire must be reconnected at the boiler or wiring centre to be brown (live) blue (sleeved with brown) for switched live call for heat, and g/y earth, tested for earth continuity back to the main earth terminal. The CM907 is battery powered and does not need a neutral so the blue wire can be repurposed as long as it is sleeved.

 

[Charnwood]

It works and has done for 8 years or more.
The correctness - or otherwise - of the current set up is not the question. The question is, can I fit a CM907?

 

[OwainDIYer]

It works and has done for 8 years or more.
The correctness - or otherwise - of the current set up is not the question. The question is, can I fit a CM907?

You can fit it in the sense that it will work.

You should not fit it because someone in future, thinking the g/y is earth, might use it to connect to the metal case of something. When the stat calls for heat the metal case of that something would then become live and dangerous.

Especially as there is no need to install new cable, there is no good reason for not doing the job properly.