Replacing (very) old thermostats for electric underfloor heating

[zcrar70]

I've just moved into a flat with electric underfloor heating. The heating is separated into zones (living room, bedroom, kitchen + hallway, bedroom 2) and each zone has its own thermostat. The underfloor heating circuit is separate from the mains electricity circuit.

The thermostats are the original 1962 (analogue) model from when the flat was built (EKCO brand - this stopped existing in the 80s I think.) I'd like to replace them with more modern digital equivalents (with timers and what not.)

The problem is that the EKCO thermostats only have 2 wires leading into them (i.e. 2 connections), and most modern thermostats seem to require 3 (live in, live out, neutral.) Is that correct?

If so, I'd need to rewire. How would that work:
live in: heating live in (i.e the first existing wire)
live out: heating live out (i.e. the other existing wire)
neutral: neutral wire from the heating circuit (which would require quite a lot of work to get to)

Sorry if this a very basic question.

 

[telectrix]

you will have to wire them with 3 core/E

 

[zcrar70]

you will have to wire them with 3 core/E

Thanks - my question was really about what the circuit should look like:

currently

            ---------
 mains
            ---------

            --------- [live/in]thermostat[live/out] ---------
                                                            |
 heating mains                                              | u/f heating
                                                            |
            -------------------------------------------------

new

            ---------
 mains
            ---------

            --------- [live/in]thermostat[live/out] ---------
                                     |[neutral]             |
 heating mains                       |                      | u/f heating
                                     |                      |
            -------------------------------------------------

Does this look right?

What I'm trying to find out is:
* am I correct that most/all digital 'stats need 3 wires
* if so and I need to rewire, is my diagram above correct?

I don't really know where the neutral wire is currently (the current wiring is all under floors or in walls), so I'm just trying to work out how much work this is going to be and whether I can do it myself (if not, we may have to live with the analogue 'stats for a bit longer!)

Apologies if I'm not expressing the problem well (and please excuse the terrible diagram!)

 

[telectrix]

basically, the old stats are just a bimetal switch, live in/live out.

the new stats have electronic modules and as such need a LandN to function. so there is L in, N in, L out. the terminals are identified in the manufacturesrs instructions. however, you can still obtain the 2 wire stats, look a bit more modern. ( i have not mentioned CPC or earth for clarity)

 

[zcrar70]

basically, the old stats are just a bimetal switch, live in/live out.

the new stats have electronic modules and as such need a LandN to function. so there is L in, N in, L out. the terminals are identified in the manufacturesrs instructions. however, you can still obtain the 2 wire stats, look a bit more modern. ( i have not mentioned CPC or earth for clarity)

That's brilliant, thanks telectrix - do you happen to know which brands still manufacture 2 wire 'stats for electric underfloor heating? I found the Honeywell ones (CM90x-CM70x) but they seem to be boiler-specific (they use TPI, which sounds boiler-specific.) Or could I also use something like that as a replacement?

 

[mark ju]

might want to check the rating on any new stat. when i have fitted them before we used stats supplied by the ufh company that could handle the load. another time we used a two wire digital programmable stat that operated the ufh via a contactor fitted near the consumer unit

 

[zcrar70]

might want to check the rating on any new stat. when i have fitted them before we used stats supplied by the ufh company that could handle the load. another time we used a two wire digital programmable stat that operated the ufh via a contactor fitted near the consumer unit

good tip, thanks - I'll make sure to check the rating on both the old stat and the new one