How do I set the two programmers on my CH+HW system

[silverfox2019]

The CH+HW system in my new home has a programmable room stat (a Honeywell CM921) downstairs and a 7 day programmer (a Honeywell ST6400c) upstairs in the airing cupboard housing the HW cylinder.

I'm wondering how best to set the CH on periods for the times I choose. For example, is it best to set the CH timings on the ST6400c to be always on 24/7*365, then control the CH timings soley using the CM921. Or would that be inadvisable. What should I do.

 

[charlie275]

What should I do.

Only you can decide. Just do whatever is most convenient.

If it's too confusing, replace one or other unit, though you'll still have the dilemma of which to replace.

If you can find the user manuals - there's often a button sequence to access an "installation mode" to enable single channel operation (though it may need re-wiring), and maybe something similar on the wall stat to disable the time feature.

 

[ianmcd]

Are you sure that the CM921 doesnt just control the downstairs heating and the ST6400C controls the upstairs and HW ?

 

[JohnD]

In my house, the programmable room stat replaced an older simple stat.

So the boiler programmer is just set to "CH 24hr on"

And the stat controls the times

I thought that was very common?

Maybe yours is like that. Try it.

 

[silverfox2019]

Thank you for your helpful comments.

 

[flameport]

The CH+HW system in my new home has a programmable room stat

There is a significant difference in using a programmable thermostat compared to an old timer/programmer system.

Timer was 'at 6pm I want the heating to turn on'. At 6pm, the boiler will turn on. A thermostat if fitted will switch the system off when the set temperature is reached.

Programmable thermostat is 'at 6pm I want the temperature in the house to be 20C'
The boiler may turn on then, or it may turn on before, or after, or not at all. How long the boiler stays on will also change.
The point is you are not setting the time for the heating to operate, just the temperature you want at a certain time.