Wiring a wireless thermostat to a pump on a underfloor heating system

Rich Berry · 12 Dec 2018

Please help.

My wireless stat packed up for my underfloor heating, so bought a Salus RF 500 to replace it, but the wiring is completely different.
The underfloor heating is run off my combi via a manafold. There is a pump on the manifold which needs to be turned on and off via the stat for the underfloor to work.

Have wired it up and stat is powered and turns on but doesn't run the pump.

Stat has live and neutral connection in and Com & NO out. How do i wire the pump in to get it working?

stem · 12 Dec 2018

Hi Rich

welcome to he forum

Unfortunately, there are so many ways this this could be wired. It's impossible to tell from the information you have given.

Your question would be a bit like asking what route you should take to travel to Cardiff, but not saying where you will be starting out from, or what form of transport you intend to use.

If you post details of the existing thermostat receivers make and model, and how it was originally wired in then someone may be able to help.

Wire colours won't help as they would have been chosen by the original installer and vary from installation to installation. It's where they were connected to that will help.

Rich Berry · 12 Dec 2018

Thanks for your reply sadly I disconnected the previous stat and because it bore no resemblance to the new one did not pay attention. The mains feed has a live, neutral and earth the pump has the same feed live neutral and earth. The earths both go to the pipework leaving just lives and neutral. I have connected the mains feed into the live and neutral and have power just need to know how to wire the pump so that the stat can switch it on and off?

oldbutnotdead · 12 Dec 2018

So there are 2 bits of 3 core cable at the position of the old thermostat? Depending on the design of the old stat, one of those 3 core cables is most likely power supply for the thermostat, the other will most likely be live from the boiler and return to the pump.
It is unwise to assume (in setups like yours) that because a core is red (or brown) it will therefore be live. There will be a wiring centre somewhere, find it and determine (using your multimeter) what goes where, guess and go is unwise.

Rich Berry · 12 Dec 2018

The pump is completely separate from the boiler and is just for the underfloor (boiler has separate pump and stat)

ericmark · 12 Dec 2018

Reading the instructions it seems you have 4 connections on the thermostat, N/O, Com, L, and N, so both earths together, both neutrals into N, line feed into both L and Com with small link wire, and line feed to pump into N/O, I will guess you have missed the link wire?

Note:- since neutral is technically considered live, the phase conductor is called line today, not Live, however old books will still call it Live.

Rich Berry · 12 Dec 2018

Ok the link is where to NO terminal?

Really appreciate your help here

flameport · 12 Dec 2018

Rich Berry said:
Ok the link is where to NO terminal?

It may not need the link.
Guessing what goes where is a sure way to destroy things.
You must find out what the other end of those cables are connected to.

Rich Berry · 12 Dec 2018

Cable into the pump goes to L N and Earth cable from mains is the same

oldbutnotdead · 12 Dec 2018

Ah we have progress. So you know for certain that 1 of those cables (we'll call it phase) is connected to power somewhere (LNE) and the other (call it load) goes direct to the supplementary pump for the underfloor heating ?
As @ericmark already said,

Connect L, N and E from the phase cable to the L,N,E terminals on the thermostat.
Connect N from the load cable to N on the thermostat as well
Connect E from the load cable to E on the thermostat as well
Put a link between the L terminal and the COM terminal on the thermostat (short bit of cable)
Connect L from the load cable to NO on the thermostat.

If you've ID'd the cables correctly then it will work. If you haven't ID'd the cables correctly there may be a bit of a bang as a fuse fails/MCB trips, if the power to the thermostat comes via the boiler (which would be odd but possible) then you could trash the control card in the boiler as well.

Rich Berry · 12 Dec 2018

oldbutnotdead said:
Ah we have progress. So you know for certain that 1 of those cables (we'll call it phase) is connected to power somewhere (LNE) and the other (call it load) goes direct to the supplementary pump for the underfloor heating ?
As @ericmark already said,

Connect L, N and E from the phase cable to the L,N,E terminals on the thermostat.

Connect N from the load cable to N on the thermostat as well

Connect E from the load cable to E on the thermostat as well

Put a link between the L terminal and the COM terminal on the thermostat (short bit of cable)

Connect L from the load cable to NO on the thermostat.

If you've ID'd the cables correctly then it will work. If you haven't ID'd the cables correctly there may be a bit of a bang as a fuse fails/MCB trips, if the power to the thermostat comes via the boiler (which would be odd but possible) then you could trash the control card in the boiler as well.

Sorted Thank you

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Wiring a wireless thermostat to a pump on a underfloor heating system

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