Replacing a Honeywell T6360B with a CM907?

[mjsp]

Hello.

I would like to improve my CH system to have a more intelligent thermostat. Currently the CH and HW are both controlled on a Honeywell ST6400C timer near the boiler, while this also connects to a simple T6360 room thermostat in the hallway to control the CH. I want to have more control over the thermostat like having a cooler temperature maintained at night without necessarily being 'off', in addition to holiday/party buttons for temporary changes to the programme.

The following items form part of my existing system:
Honeywell ST6400C 2-channel timer module
Two Honeywell V4043H valves, I imagine one is for HW and one for CH, but not entirely sure
Rectangular Honeywell box where everything is wired up, I assume this is the 10-point connector jobby in the diagrams
Some other stuff like a pump, big water tank, a boiler that powers both the HW and CH, all of which I am hoping is irrelevant to my question
One T6360B room thermostat elsewhere (in the hallway)

I *think* I have exactly the setup listed as 'S-Plan' on this page, but it is not quite clear to me:
https://products.ecc.emea.honeywell.com/europe/pdf/st9000wired-50022736005-uk07r0812.pdf

In hope that the above is enough to go on...

What do I need to change? My guess would be that I could replace just the T6360B room stat with the more intelligent CM907, then tell the ST6400C that CH is always 'ON' so as to bypass its timer, while that would then go through the CM907 that would act as the main control for CH. And, continue to use the ST6400C for HW timer. Would this work / are they compatible?

Any confirmation of the above, or other suggestions about what I should be replacing and with what, would be very much appreciated.

The closest I have found to someone else using similar kit is on the following thread, but his initial failure before he had replaced the ST6400 with a ST9400 concerns me:
//www.diynot.com/diy/threads/r...60-with-a-cm907-problems.386325/#post-2966166

 

[D_Hailsham]

My guess would be that I could replace just the T6360B room stat with the more intelligent CM907, then tell the ST6400C that CH is always 'ON' so as to bypass its timer, while that would then go through the CM907 that would act as the main control for CH. And, continue to use the ST6400C for HW timer.

That will work.

Wire as follows:

T6360B - CM907
1 ------------A
3 ----------- B
2 ----------- Not used. Make safe, e.g terminal block

At the ST6400C, move wire from terminal 4 (CH ON) to L. You then don't need to set CH to always on.

 

[mjsp]

That will work.

Wire as follows:

T6360B - CM907
1 ------------A
3 ----------- B
2 ----------- Not used. Make safe, e.g terminal block

At the ST6400C, move wire from terminal 4 (CH ON) to L. You then don't need to set CH to always on.

Fab. That all makes sense and wiring is as I expected. Thanks for your help, will purchase.

...no idea why the guy in the other thread had his issue.