Honeywell CM927 room thermostat and “System Synchronisation”

[Oaklyn]

Hello,

My gas central heating system boiler has two main heating circuits, one for the upstairs and another for the downstairs. Each of the heating circuits are independently controlled using motorised valves which are opened and closed under the control of two Honeywell CM927 room thermostats each of which has its own “control box” (fixed to the wall near the boiler) which is “bound” to its own CM927 room thermostat (which is located in a room).

I have been looking at the “Wireless Installation Guide” for the CM927 - this is a document meant for installers and not “end users” like me. However it shows how to set the CM927 into “Installer Mode” to give access to the “Installer Parameters”.

In section “4.5.2 Category 2 - System Settings” of the Installation Guide there is the following parameter listed :

Parameter : System Synchronisation

Parameter No : 6:Sn

Factory Default Setting : 0 - Standard operation of the Room Unit

Optional Setting : 1 - Room unit configured as a Synchroniser

Despite hours of searching I can't find any reference to CM927 Synchronisation and what it is/does anywhere on the internet.

Please can I kindly ask if anyone knows what "System Synchronisation" is and what does a room unit do when it is configured to be a “Synchroniser”?

Is any additional equipment needed to use the “Synchroniser” functionality?

Thank you in advance for your kind assistance.

 

[JonathanM]

This thread might help for starters:

https://www.diynot.com/diy/threads/can-i-use-cm927-to-open-2-zone-valves.249618/

EDIT: from post#3

The problem with that is that the valve can be opening and closing frequently due to the way the CM927 turns the boiler on and off to maintain the correct room temperature. This means one stat could be trying to turn the boiler off at the same time as a second stat is trying to turn it on.

The way to overcome this is to configure one CM927 as a master/synchroniser and the other as slaves. The CM927 relay units just control the opening and closing of the zone. An additional relay box acts as the boiler controller.

 

[Oaklyn]

This thread might help for starters:

https://www.diynot.com/diy/threads/can-i-use-cm927-to-open-2-zone-valves.249618/

EDIT: from post#3

Thank you for your reply.

In the example given (above) two (or more) CM927's are linked to the same zone (or zone's combined) with the "master" being the ultimate controller of the zone(s).

I was hoping that the "Synchronisation" mode meant there could be one CM927 per zone and the one set as the master would "sync" with the other CM927 on the other zone so the "heat cycles" were synchronised and when one CM927 (downstairs - e.g. the master) decided to come on it would tell the other CM927 (controlling the upstairs) and the upstairs would come on (if necessary) at the same time as the downstairs so the boiler only fired once. At the moment I am finding that the downstairs comes on firing the boiler and when that has finished the upstairs them comes on with the boiler effectively firing again (e.g. running constantly) rather then the two zones working together (i.e. "synchronised") so the boiler only comes on once to provide heat to both zones (if necessary). (Did I make that clear?)

 

[JonathanM]

I’ve got to start by saying that I was really just trying to find a previous post which might be relevant. I have no experience of anything this complex. I think you are being clear about what you want. But I actually read the post from @D_Hailsham differently to you, and I took it to mean that the proposal he suggested would accomplish what you want. I think I read somebody mention that he no longer posts.

However, I think all the kit mentioned has now been superseded. Whether you can still get it to work with any new bits you might need is not something I would know about.

 

[Oaklyn]

Thank you for your reply.

To me, as an "end user" it seems strange that the concept of "System Synchronisation" could be listed as a feature of the CM927 yet there is seemingly no documentation whatsoever available about it on the internet. A product produced without any information as to what it does or how to use it???

Do other manufacturers, other than Honeywell, have something similar to Synchronisation? Perhaps other manufacturers call it by a different name?

 

[MJN]

At the moment I am finding that the downstairs comes on firing the boiler and when that has finished the upstairs them comes on with the boiler effectively firing again (e.g. running constantly) rather then the two zones working together (i.e. "synchronised") so the boiler only comes on once to provide heat to both zones (if necessary). (Did I make that clear?)

Assuming you want independent control of each zone then the operation you’ve described there is surely exactly how you want it to behave. The calls for heat are based on current temperature and, in the case of your TPI stats, a periodic firing sequence calculated to maintain the target temperature to a high degree of stability. Tying the operation of the two stats together in any way will undermine one one or both of their ability to operate with the freedom of control they need giving rise to inevitable compromise. Both stats/zones calling for heat at the same time should be left to coincidence, not design, unless you’re happy with what in effect would be a single zone in which case you could remove the superfluous stat entirely.

Perhaps if it wasn’t for the TPI operation it wouldn’t be quite so obvious the amount of mismatched/out-of-sync firings between the two zones, but that’s something of a key feature of your stats and so goes with the territory.