Digital room thermostat

[Kimberley88]

Changing my boiler looks like its not going to be a viable option, so plan B is to change the old bits of the CH system to narrow down the problems.

First job to change the old honeywell thermostat for a digi sunvic one.

The problem I now have is the honeywell has 2 cables going to it, one from the programmer and another. Currently set at

programmer red in 1
other red in 3
Both blacks in 4


The Sunvic has 3 connections

3 = C
2 = ON
1 = OFF


Anybody know which connections go where because there is no space i the sunvic to have two blacks in one hole so I guess one cable is no longer required as sunvic has batteries.

Help appreciated.

 

[ArtfulBodger]

Did you buy a programmable thermostat or just a stat?

You are attempting to replace a 230/240V stat with a volt free relay which means you are going to have to do a bit of work to get it working.

If it's just a digital stat then you are going to have to use the relay to provide a switched live when heat is required. The SL should then be used to power your motorised valve which in turn will switch on your pump & boiler. So, live from programmer to C(3) and SL from stat via ON(2).

If it's a programmable stat then you can bypass the programmer and use it to provide a SW direct to the motorised valve. Same wiring as before.

Of course, how you provide the neutral and earth is something that you will have to work out for yourself.

 

[Kimberley88]

Thanks Artfulbodger

It was just a digital stat, don't fancy messing about so will take it back, can I get a digital stat that will be a straight swap? if not I will just get an ordinary mechanical stat.

At least I now know the stat has a problem because the digi is sitting on top of the honeywell reading 24 degrees and the honeywell is showing 15 and the heating has come on again

 

[ArtfulBodger]

Thanks Artfulbodger

It was just a digital stat, don't fancy messing about so will take it back, can I get a digital stat that will be a straight swap? if not I will just get an ordinary mechanical stat.

At least I now know the stat has a problem because the digi is sitting on top of the honeywell reading 24 degrees and the honeywell is showing 15 and the heating has come on again

There won't be straight swap but it's easy enough to do. From what you describe the existing stat is switched on via the programmer which in turn sends power to the valve. It doesn't sound like it goes back to the wiring centre, but as I can't see it then obviously I don't know.

The existing stat require L, N & E. The digital stat doesn't 'cos it's battery powered and all it does is provide a relay for your use. This can be used to provide a switched live to the valve.

The valve requires a neutral and earth of course. So, all you have to do is work out how to disconnect the old stat, install the new and provide the necessary connections to the valve.

You might be better off just getting a powered stat, just about anything with "230" in the product code will be suitable. It helps to have a multimeter to use when doing this stuff!