Sunvic Room thermostat replacement

I replaced my 30 year old satchwell TLX2356 (now known as Sunvic) with TLX9201. nothing happens after following guidance on the net. The LED light does not come on.

This is what I did in order.

1) power off mains
2) disconnect old TLX2356
3) connect new TLX9201, Brown to Term1 1, Earth to Term 3, Blue to Term 4
4) power back on and nothing happens. Checked all the fuses and all okay. I noticed there was no power to Term 1 with a tester.

I tried again with another TLX9201 but same results.

In the old TLX2356, I noticed that the blue was in Term 1, brown in term 3 and earth wire on the metal back plate.

I am not sure if I should connect the Brown in Term 2?

Any advice greatly appreciated in advance.

Here is a pic of old TLX2356 (Pic in anti-clockwise....don't know how to turn up)


Here is a Pick of the New TLX9201

First of all, you need to determine what the earth wire actually is. If it is physically connected to earth at the 'non thermostat' end, under no circumstances should it be connected to anything other than an earth. If there isn't an earth connection required by the new thermostat, then it should be insulated and tucked safely out of the way.

If it is connected to earth and you have put it in terminal 3 and turned on the power, whilst the thermostat in the 'call' position you will have created a direct short circuit and blown either the fuse, damaged the timeswitch (if there is one) or even the new thermostat.

Your original wiring if correctly installed based on the terminals you describe it as being connected to would indicate that: Brown = Live. Blue is being used as the 'switched live'. Earth is used as earth. There is not a Neutral.

The wiring on the old TLX2356 is: Terminal 1 = Switched Live (aka Demand), and Terminal 3 = Live Supply
The wiring on the new TLX9201 is: Terminal 3 = Switched Live (aka Demand), and Terminal 1 = Live Supply (do not use terminal 2 for anything. This is used for cooling as opposed to heating)

The instructions for the TLX9201 show that there should be a neutral in terminal 4 for correct operation of the new thermostat but you don't appear to have have one, so this is likely why the LED light doesn't come on. If so, you will need to run a neutral wire, or change the thermostat for one that only needs a live and switched live connection. (There are lots to choose from)

The missing live is a concern. It suggests that you have 'blown' something upstream. However it would only be 'live' when an associated timeswitch is 'on'.

If you don't understand what the wires actually do and how the thermostat works, you should really get someone who does to investigate, swapping wires from terminal to terminal hoping that you will get the right combination by chance can be both expensive and dangerous.

Stem, Many thanks for your reply. You are a genious that even 2 qualified plumbers and 1 electrician could not solve. I did just as you said, disconnect the earth and I am now beaming with joy.

OK, it may work, but you are still missing the neutral connection. Whilst it's not essential, it is there to operate a device known as an 'accelerator' which improves the switching accuracy of the thermostat.

Many thanks. Advice greatly appreciated