Fitting/wiring a timer/thermostat on a radiator circuit

27 Nov 2019
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United Kingdom
I need some advice on the fitting/wiring of a timer/thermostat to replace a room thermostat , first an explanation of my current system:

I have underfloor heating with 8 zones downstairs, and a separate radiator circuit upstairs. The downstairs UF heating has a simple thermostat in each room plus one setback thermostat for frost protection and the upstairs radiator circuit is controlled from one room thermostat plus individual TRVs on each radiator. I have an oil fired boiler which feeds a large energy store hot water tank, hot water is produced by running cold water through a coil in the hot water tank. The water tank is kept constantly hot by the boiler which cycles in and out to keep the tank water at the right temperature.

There is a Danfoss TS715 single channel time switch that controls when the underfloor heating and radiators are on.

I want to be able to control the upstairs radiator circuit with its own timer - at the moment if I have the UF heating on during the day I shut the radiator circuit off by adjusting the room thermostat upstairs - which is a pain as I don’t always remember to do it and I have to readjust an hour or so before going to bed - which I also don’t always remember to do.

I’ve had a look at the wiring centre for the heating system and it has various sections as follows:

  1. Radiator timeclock/stat
  2. Floor pump
  3. Floor heating time clock
  4. Setback Thermostat
The current wiring setup has live and neutral and earth from the radiator circuit thermostat going into the 1. Radiator timeclock/stat section (see pic) but what I assume is the S/L cable (black) goes into the 3. floor heating timeclock section along with the S/L cable from the Danfoss timer (see pic 2).

If I replace the room thermostat with something like a Salus RT510RF I can then program the radiator timing separately and also have the thermostat wireless which will be an advantage as the current wall thermostat is in a bedroom behind a wardrobe and is not easy to get at!

Can I therefore wire the RF receiver into where the current thermostat is positioned (there are 4 wires to this thermostat but only 2 are used at the moment) and then will I need to move the S/L cable from its current position (into section 3 as above) to section 1 - radiator timeclock stat?

I am reasonably competent but I may get an electrician to do the wiring if I am not 100% sure sure.

Thanks in advance for advice/help

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It’s looking more complicated! Some additional info:

The room thermostat is wired to the wiring centre via another terminal box, only 2 of the 4 cables are used, the earth is not connected at the thermostat end and there is a grey cable that is not connected at the terminal box. From the terminal box to the wiring centre 3 cables are connected to the rad timeclock stat section an additional the fourth to the underfloor heating section as per my description above. How would have to wire in the new grey cable from the new thermostat?

I’ve found the electrical installation manual and there are some diagrams but I don’t think my system is exactly as per the various setups and as it is so complicated I think I’ll definitely have to get an electrician or probably a heating engineer who understand nu-heat systems to do the job. I’ve posted a couple of pictures of the diagrams and the additional terminal box. If anyone thinks its relatively simple let me know and I might attempt it!


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