Honeywell CM927 Advice

[Eng33]

Currently have a Honeywell ST6400C 7 day programmer controlling CH and hot water (oil fired boiler). Rads have TRVs but there’s no room stat. As I refurbish and extend the house, I really fancy installing a CM927 wireless controller, but in all the spec info I have read on this unit, there is no mention of controlling hot water. A friend has one and swears by it, but he has a combi boiler so no requirement for controlling hot water.

Am I therefore correct in thinking that this unit would not be suitable for my system? Any suggestions for alternative if not, prefer a wireless stat type.

Thanks.

 

[Eng33]

Doh.... note to self, use the search function next time....

Just found the answer to my question in a very useful thread replied to by 'D_Hailsham'.

Do have one further question though, if I do install a CM927 and use it in conjunction with my current ST6400C to control the hot water, will i need to replace my existing 3-port motorised valve, with two 2-ports valves?

Thanks.

 

[D_Hailsham]

if I do install a CM927 and use it in conjunction with my current ST6400C to control the hot water, will i need to replace my existing 3-port motorised valve, with two 2-ports valves?

Thanks for the compliment

The simple answer is no.

Read Honeywell Application Guide 109

There is an error in their wiring diagram. Terminal 7 also needs to be connected to the HW OFF terminal of the programmer.

 

[Eng33]

Thanks for the reply.

Just out of interest, assuming I've understood correctly, why would you chose to install an S-plan system using two 2-port valves, when a Y-plan system uses just one 3-port valve?

 

[gas4you]

Set the ch on the 6400 to constant (24hr) setting then fit a CM 927 to control the temp/times of the ch. Problem solved and about 30 mins wiring needed.

 

[D_Hailsham]

why would you chose to install an S-plan system using two 2-port valves, when a Y-plan system uses just one 3-port valve?

The method used to hold a 3-port valve in the mid-position means that the motor and other electrical components are more likely to fail sooner than in a 2-port valve. Also, if you have more than one heating zone, you have to use S-plan, each controlled by its own zone valve.

Set the ch on the 6400 to constant (24hr) setting then fit a CM 927 to control the temp/times of the ch. Problem solved and about 30 mins wiring needed.

That's the lazy plumber's way of doing it; it will take no longer to do it the correct way.

 

[ChrisR]

That's the lazy plumber's way of doing it; it will take no longer to do it the correct way.

Not incorrect, just different. Better g4y's way in my opinion.

 

[D_Hailsham]

Better g4y's way in my opinion.

And when someone "accidentally" changes the old time switch from Constant CH to Twice or Once and no one can work out why the CH is not coming on properly?

The only difference in the two methods of wiring is where the 230v supply for the new programmer is obtained: from the CH ON connection of the old programmer or from the main live connection of the terminal strip.

 

[Eng33]

Better g4y's way in my opinion.

And when someone "accidentally" changes the old time switch from Constant CH to Twice or Once and no one can work out why the CH is not coming on properly?

For that reason, I have decided to ditch my original ST6400C all together, and install a cheap single channel ST6100C or similar programmer for the HW. Much tidier solution I think, as well as being 'idiot proof'

D_Hailsham - I assume the best way to wire all this lot together is to use one of Honeywell’s 10 way junction boxes?

 

[D_Hailsham]

I have decided to ditch my original ST6400C all together, and install a cheap single channel ST6100C or similar programmer for the HW. Much tidier solution I think, as well as being 'idiot proof'

Quite right - that's what I did; picked up a cheap one on Ebay. The other methods just save money!

I assume the best way to wire all this lot together is to use one of Honeywell’s 10 way junction boxes?

Yes