Honeywell CM907

[whisperingbob]

I have just fitted this new thermostat but I am having problems.

There were four wires in the original mechanical thermostat, one an earth, one (presumably) a neutral and the other two to switch the boiler. I have isolated the earth and neutral, and connected the other two to the A and B terminals.

The boiler which is a new Vailant combi starts briefly and then stops so I assume the wiring is wrong.

How should I have wired it?

How do I get the thing open again without breaking it? The two halves seem not to want to part company.

 

[Dan Robinson]

What was the original one? What terminals had what wires?

 

[whisperingbob]

I got it open:

There are two tiny slots at the top of the battery compartment - insert a small screwdiver and Bob's your Uncle.

Still not sure about the wiring though

 

[whisperingbob]

The original was also Honewell but I don't know the model. A square box with a dial to set the temp is all.

There are 5 terminals - from left to right - earth & 2 together (I assumed earth and neutral), then 3,4 and 1. The other two wires were in 3 and 1

 

[Dan Robinson]

1 and 3 go to A and B.

Earth and Neutral are to be made safe.

 

[whisperingbob]

Thanks for the prompt response.

When i finally got it open I found that one of the wires wasn't making a good contact so I made it good and now it works.

Phew: