Wiring Honeywell CMT927 RF and Separate programmer to a combi

[JoeJoe]

Just bought the above wireless thermostat and a separate programmer to control my combi. Both are 7-day ones. The reason for this setup is that we do know exactly where we want to programmer/controller to be positioned (for convenience reasons), but am not sure exactly where to position the thermostat. The house is quite drafty, so we may have to try a few places before we find the best one.

I run 2 x 2.5mm Twin & Earth cables from the boiler to the position where the programmer is to be located (I can get mains feed either from the boiler end, and also from near where the programmer is going to be located). I also intend to fix the CMT927 receiver unit very close to the programmer (~1m).

Does that make sense as a set up?

[Roger Mills]

Not a lot!

The wireless programmable stat is *also* a programmer. If you have two programmers in series, the heating will only come on when *both* are on. The fixed programmer is a total waste of time and money - and will have to be set to 'constant' to allow the programmable stat to work. So replace it with a short piece of cable!

The base unit for the stat should be as close to the boiler as possible, to minimise the wiring needed. The sensor unit - which, AIUI also incorporates the display and programming buttons - can be unhooked from its perch and taken to your 'convenient' position when you want to change the programme - and then returned.

[JoeJoe]

Thanks for taking the time to reply, but I perhaps I didn't explain what we were trying to achieve properly.

We (well, she... always cold...) tend to use the override feature (i.e. turn it to "constant on" or to "1hr boost") pretty often, and therefore we want the controls to be in a convenient position. As the downstairs is drafty, we may end up with the stat in the upstairs landing, so we don't want to have to use it as the main control for the system. I agree that we could potentially use a much cheaper/simpler wireless stat, even without any real programming - but we got a very good deal on the 927, so we got it anyway.

The plan is to set the stat to pretty much "always on" temperature throughout the day, and do the time/day control from the conveniently positioned programmer. The reason we wanted a little smarter stat is to allow us to experiment with different temperature settings for, say, morning and evening.

Sorry for not explaining this earlier.

Does it make more sense now?

[Roger Mills]

I can see what you're setting out to achieve but, in your position, I'd be attacking the drafts first before worrying about over-complicating the CH control.

By having another timer in series with your programmable stat you will negate some of the features of the stat - such as its ability to act as a frost stat in its 'off' state.

If you want to boost the temperature above the current stat setting at a time when the main timer is on, you'll have to go to the programmable stat anyway!