Replacing a 3-wire thermostat with a 2-wire

[Mark1955]

I am planning to replace an old mechanical room thermostat with a new digital one. The old one had three connections, the new one only two.

Looking through the posts on this forum, it seems that I don't need the neutral connection anymore and it should be disconnected and tidied away.

This picture shows the old connections/circuit diagram:

Untitled

• Mark1955
• 16 Dec 2013
• 1

This picture shows the new circuit diagram:

Untitled

• Mark1955
• 16 Dec 2013
• 1

Can somebody confirm that what I need to do is:

1. take the wire that is currently connected to "4" and connect it to "W";
2. take the wire that is currently connected to "6" and connect it to "R"; and
3. neatly terminate the wire that is connected to "2".

Thanks

 

[D_Hailsham]

Which make/model new thermostat are you using?

 

[Mark1955]

Its the Wickes one. TH147E.

 

[D_Hailsham]

Its the Wickes one. TH147E.

Can't find it on their website!

 

[Mark1955]

No, I couldn't either.

When I googled TH147E, I came up with AUBE Technologies and the documentation on that website is the same as I've got from Wickes. The Wickes website only has a load of other makes none of which were available at our local Wickes, this was the only non-programmable digital version that they had in stock.

 

[D_Hailsham]

Can somebody confirm that what I need to do is:

1. take the wire that is currently connected to "4" and connect it to "W";
2. take the wire that is currently connected to "6" and connect it to "R"; and
3. neatly terminate the wire that is connected to "2".

Nearly correct.
1. take the wire that is currently connected to "2" and connect it to "W".
2. take the wire that is currently connected to "6" and connect it to "R".
3. neatly terminate the wire that is connected to "4"; e.g in a terminal block.

W and R are interchangeable as are 2 and 6.

 

[Mark1955]

Can somebody confirm that what I need to do is:

1. take the wire that is currently connected to "4" and connect it to "W";
2. take the wire that is currently connected to "6" and connect it to "R"; and
3. neatly terminate the wire that is connected to "2".

Nearly correct.
1. take the wire that is currently connected to "2" and connect it to "W".
2. take the wire that is currently connected to "6" and connect it to "R".
3. neatly terminate the wire that is connected to "4"; e.g in a terminal block.

W and R are interchangeable as are 2 and 6.

Thanks for the response.

The reason I connected "4" to "W" and not "2" was because of the "blocks" in the circuit diagram on the old thermostat. I assumed that the one between "4" and the switch was equivalent to the "load" between "W" and "L2" on the circuit diagram for the new thermostat and that the symbol in the one outside "2" was an earth symbol.

In your opinion, what are they?

Sorry to be nervous but I'm not quite sure what might happen if I get it wrong.

 

[D_Hailsham]

I identified the old stat, from the pic, as a Landis & Gyr RAD5. The connections on this are:

2 = Call (to boiler)
4 = Neutral
6 = Common (from timer)

The new stat does not require a neutral, so the wire to 4 is made safe.

That leaves 2 and 6 which can be connected to W and R, either way round.

 

[Mark1955]

I identified the old stat, from the pic, as a Landis & Gyr RAD5. The connections on this are:

2 = Call (to boiler)
4 = Neutral
6 = Common (from timer)

The new stat does not require a neutral, so the wire to 4 is made safe.

That leaves 2 and 6 which can be connected to W and R, either way round.

Thanks for your help and because you could identify the stat from a picture, I'm certainly impressed.

 

[RF Lighting]

You need to get an electrician to re-configure your wiring. You are currently useing a BARE copper wire as a LIVE conductor.

Totally unacceptable and down right dangerous.

 

[Mark1955]

You need to get an electrician to re-configure your wiring. You are currently useing a BARE copper wire as a LIVE conductor.

Totally unacceptable and down right dangerous.

Thanks for your comment.

I've traced the wiring back and there's a place only a few feet from the thermostat where ithere is a strip connector with yellow, blue and red wires connected to bare, red and black which are then connected through to the thermostat (about four feet). Obviously at some point in the past the thermostat has been moved and the wires extended.

I can reconfigure it at the strip connector so that the two active wires are red and black.

Its been that way a long time (that doesn't make it right).

 

[D_Hailsham]

I can reconfigure it at the strip connector so that the two active wires are red and black.

To do the job properly you should cover the black with some red or brown sleeving to show that it is a live wire.

 

[Mark1955]

OK I'll do that.

 

[RF Lighting]

I can reconfigure it at the strip connector so that the two active wires are red and black.

To do the job properly you should cover the black with some red or brown sleeving to show that it is a live wire.

And then sleeve the bare copper wire with green and yellow sleeving at both ends, and ensure it is connected to earth at the supply end, even if the new stat does not require an earth connection.