Thermostat wiring advice needed.

[Muddymike]

Having just bought a Salus programmable wireless central heating room thermostat I'm a little confused by the connections to the system.

I would like to simply mount the receiver unit where the old (ancient) Satchwell dumb thermostat is as it in a good central point in a hallway that should communicate well to all downstairs rooms.

The old one has three wires Rd, Blue and Yellow connected to three terminals just numbered 1, 3 & 4.

The new unit has four terminals named and described in the vary basic instruction leaflet as. NO = Switch terminal Com = Common switch terminal L = Mains live N = Mains neutral

I'm thinking the; Blue wire goes to Mains neutral. Red to Mains live & Common switch terminal Yellow to Switch terminal

But am not confident hence seeking advice.

Mike

[alan_m]

Red to L Blue to N Yellow to NO

And an additional short piece of wire wire from L to Com

[Dave W]

As you don't say what model you have, I looked on the Salus website to find one with four terminals, e.g. the RT500RF. You will have to consult your boiler manual to find out what the red, blue and yellow wires have on them.

However, googling for Satchwell leads me to believe that there is mains (not 24V) on your three wires, in which case I suggest Red to L, Blue to N and Yellow to NO. It's not clear, but as the COM terminal is described as "Linked live feed". it's probably already connected to L.

[Michael Chare]

I would want to check how the wires are connected at the other end. I don't think that there is any standard.

The boiler may have an on/off programmer at the other end. If this goes off the Salus may not get any power which it may not like.

[Tim Watts]

The colours and terminal numbers are rather unrealiable and variable. You'll be best to test which ones are Live, Neutral and control to boiler.

But essentially you are correct, if I rewrite it in those terms:

L goes to permanent live N goes to neutral

L is linked to Com with a short piece of wire (this is pretty normal)

NO is your switched output to the boiler control (that last wire you have left, apart from earth).

[Tricky Dicky]

The colours you have described are the old 3 core + E and one would hope red and blue would be connected as previously described. However, that may not be the case so you must look at what those wires are connected to at the other end before you connect your thermostat.

Richard

[alan_m]

More likely com is not internally connected to live as it allows the unit to be configured in two ways dependent on the system. If 3 wires were removed from the terminals of the old thermostat it suggestsswitched live and the new unit wired in the way the OP has suggested.

[alan_m]

There is a good chance that is the arrangement. The wireless receiver will probably have two lights. One to indicate that it is getting mains voltage and the other to indicate that the thermostat is calling for heat. If there is boiler controller then the CH timing side possibly needs to be set to be permanently on so that the wireless receiver is always getting power and then let the thermostat control all of the on/off and different temperature times.

Depending on the system, turning on/off the CH heating by way of the boiler controller will also turn on/off the power to the wireless receiver. This is very unlikely to do damage to the receiver but what may happen is that the receiver when switched back on may not reliably wirelessly re-pair with the thermostat.

[Michael Chare]

I would not want to rely on chance! The Salus may not be good at time keeping if it loses power. I would think it would be happier to be connected to the mains power input for the boiler.

[Dave W]

Surely yellow was never earth? Also the old colours were red and black not red and blue.

[Dave Liquorice]

Did you miss the 3?

[Tim Watts]

Red blue and yellow for old 3 phase cable, including triple and earth. The earth was bare, or sleeved in G+Y (or green if you go back far enough).

[Muddymike]

Thanks for the confirmation guys.Its wired as per and fully functioning.

Mike

[ARW]

Assuming everything is what it should be (the OP has actually said that it is) then the blue core should have been oversleeved with black and the yellow core should have been oversleeved with red.

I have seen it happen a couple of times out of thousands of thermostats/bathroom fans etc I have looked at/replaced/worked on.

I might have oversleeved the yellow with red a few times but I never oversleeved a blue with black.

[Roger Hayter]

If the blue wire goes back to mains neutral why does it need oversleeving in black? Is it because the rest of the wiring may be still in the old colours? Couldn't you oversleeve the yellow and red with brown? Sorry, genuine ignorance here.

[Muddymike]

I just left the old colours as is and found a piece of red to bridge across to the com.

Mike