Central Heating Thermostat Replacement

[kamil99]

Hello,

Could I use your infinite wisdom, please?

I currently have an old analogue SUNVIC TLM 2253 Thermostat ( https://www.uk420.com/boards/uploads/monthly_09_2008/post-26762-1221828293.jpg ) which to operate uses two wires (red - live and blue - neutral).

I wanted to replace it with a digital programmable thermostat ( http://imgs.inkfrog.com/pix/Eglobal/HT0000601_9.jpg ).

There are four wires in total:
in use:
- red
- blue
unused:
- yellow (load?)
- uninsulated (earth?)

I tried connecting red to AC IN L, blue to AC IN N and yellow to LOAD L1.
The screen keeps flashing, but nothing is displayed. Same thing happens when I connect red and blue only. It's like if it was restarting on a loop.

I thought the thermostat was faulty and had it replaced, but it keeps doing it.

Is this information enough to tell whether such thermostat is compatible with my central heating at all? Do you know what I am doing wrong? I don't know much about electrics so I haven't tried any other wire combinations yet not wanting to break anything.

Many thanks for your help.

Regards,
Kam

 

[Blagard]

The two wires going to your thermostat are not live and neutral but live and switched live (No neutral). The blue should have been sleeved to show it is used as the switched live conductor.

To wire in the new thermostat you will need a neutral connecting

From your post you currently have running to the old thermostat a triple and earth with yellow and earth unused

I would rewire the other end of the cable so that the blue becomes the neutral the red remains live and the yellow a switched live. Then put a brown sleeve on yellow and red at both ends of the cable to show they are live conductors.

If you have any doubt now, call an electrician to do it for you.

Edit: As D_Hailsham has indicated by his questions below, you will probably be thinking of using the programmable thermostat and not using the existing central heating timer so there will certainly be changes to the wiring required at the boiler end to do the job properly, otherwise you will end up with two timers working in series!

 

[D_Hailsham]

Which boiler do you have? Make and exact model

Do you have an existing timer?

How is the Sunvic wired?

Make and model of new prog stat?

 

[ianmcd]

Blagard is spot on, your existing stat has live in and switched live out, NEVER go by a wires colour in a heating system