Wiring a Thermostat

[Daltone]

Hi Folks,

I've recently bought my first house with my fiancee! Exciting times, but it turns out that the thermostat connected to the (very old) boiler is very broken.

I want to replace it with a Honeywell CM907 (or similar - suggestions welcome!). However, I've pulled off the front of the current thermostat and found this:

That seems like a lot of live wires!

The only help I have is this:

Unfortunately, this doesn't mean a lot to me.

The wires themselves seem to be coming in from a cable that runs along the wall:

The boiler in question is a Baxi Solo 2. There is a separate hot water tank upstairs, if that makes any difference.

My question is - how on earth do I get a modern thermostat attached to that wiring? I am a bit lost.

Thanks,

Ed

 

[EFLImpudence]

Old 1 to New A
Old 4 to New B

Old 2 Should be sleeved blue to indicate it is neutral.
Not required on New so terminate in separate connector block and position safely.

 

[Daltone]

Old 1 to New A
Old 4 to New B

Old 2 Should be sleeved blue to indicate it is neutral.
Not required on New so terminate in separate connector block and position safely.

Hi,

The terminals on the old thermostat are labelled 2,1,4,3 in descending order. I am guessing you are counting the top, term 2 as "Old 1" and the bottom, Term 4, as "Old 4" - is that right?

What I would give for properly coloured wires..

 

[denso13]

Top one on the old stat is neutral as per the sticker. Should be Old 1 (second top) to New A and Old 3 (bottom) to new B.

 

[EFLImpudence]

The terminals on the old thermostat are labelled 2,1,4,3 in descending order

If correct then old thermostat wired wrongly.

Did it work backwards?
I.e heat on when turned down and vice versa.

 

[Daltone]

The terminals on the old thermostat are labelled 2,1,4,3 in descending order

If correct then old thermostat wired wrongly.

Did it work backwards?
I.e heat on when turned down and vice versa.

It was hard to tell. The guy that lived here before was excitable but ineffective when it came to DIY. It certainly didn't seem to work as it should.

Is there an easy way to work out what's what?

 

[Daltone]

Top one on the old stat is neutral as per the sticker. Should be Old 1 (second top) to New A and Old 3 (bottom) to new B.

Thanks, I'll give this a go

 

[EFLImpudence]

You could try moving the wire from terminal 3 to 4 and see if it works.

If it does then the other two must be correct.
If not ... have you a multimeter?

 

[SimonH2]

I'd suggest ...
Mark each wire before you disconnect it from a terminal. A good permanent marker should do - just put some "dots" on the wires, probably match the numbers on the terminals.