programming honeywell cm921

[paddyman89]

Hello
I want to programme my mothers honeywell cm921 so her heating comes on twice a day. Once in the morning coming on at 7.30am going off at 8.30am, then finally at night coming on at 8pm going off at 10pm. The instruction booklet does not make a lot of sense to me. A simple step by step answer would be appreciated.
There are six different default time zones in the
booklet. Does that mean it comes on at time zone one(6.30am at 21 degrees) and goes of again at time zone two(8am at 18 degress)?
and repeats that pattern for time zones 3,4,5 and 6?
Any advice would be appreciated
Thanks

 

[crockett]

Yes. 1,3 and 5 are 'on' switches. 2,4 and 6 are 'off' switches. So you have three 'on-off' times 1-2, 3-4, 5-6. Setting the temperatures at the given times utilises what is called 'Optimum Start', a facility which makes sure the temperature reaches whatever you set it at, at the time you've programmed. So, for instance, if you set 8 am as your on time, and 22 deg c as your temp, the programmer will ensure that the ambient temperature is 22 deg c at 8am, which will mean that in theory the boiler may switch on earlier than 8am if the ambient temp is less than this. If you have the 'off' temperature at, say, 18 deg c, then the programmer will ensure that the ambient temp reaches this at the off time, which, again, might mean the boiler switching off earlier than the programmed time. Apparently the programmer will 'learn' to fine tune this facility.

Hope this helps.

 

[mikely]

The thermostat does not have on and off times as such, only times at which the set temperature changes. In effect it can be made to be on and off by, for instance, setting period 1 to 20C at 7:30 am and then period 2 to 10C at 8:30am. You can also disable individual time period changes so that, for instance, only periods 1,2,5 and 6 are active.

The optimum start feature, which is worth using, has to be enabled in the Category 1 settings of the Installer mode because, in the factory default setting, it is set to off.

For advanced settings see: http://www.honeywelluk.com/Documents/Full-Install/pdf/1069.pdf

 

[paddyman89]

Thats great thanks,
Much easier in plain english, i'll give that a go, for the times i used as an example it seems best to disable settings 3 and 4? Also if i wanted to turn the heating on manually in extreme conditions (for example i walk in at 2pm and the house is cold) whats the best way of doing that? Would that be to use the manual setting and just notch up the thermostat setting a few degrees?
Thanks again

 

[MJN]

If you have the 'off' temperature at, say, 18 deg c, then the programmer will ensure that the ambient temp reaches this at the off time, which, again, might mean the boiler switching off earlier than the programmed time.

Optimum Start doesn't apply to decreases in temperature, i.e. it won't turn the boiler off early to allow a ramp down in temperature.

[...] if i wanted to turn the heating on manually in extreme conditions (for example i walk in at 2pm and the house is cold) whats the best way of doing that? Would that be to use the manual setting and just notch up the thermostat setting a few degrees?

You'd be better off leaving it on Auto and just pressing the + temperature button a few times to increase the target temp to that desired. The benefit of this strategy is that you don't need to remember to switch back from Manual to Auto and it'll just continue with the preset programme at the next temperature switching point.

Mathew

 

[mikely]

Yes, if you just want the system on twice a day like a conventional programer, disable periods 3 and 4.

At any time that the unit is in Auto mode, if you simply turn up the temperature it will stay at that level until it changes at the next programmed time period.

The idea with a programmable stat is that you don't simply turn the heating on and off twice a day like a conventional programmer. You set different temperatures at different times of day (and night) to suit your lifestyle. So if you set, say 16C during the day it will keep the house at a background level so that on really cold days it doesn't cool down too much.

 

[D_Hailsham]

for the times i used as an example it seems best to disable settings 3 and 4? Also if i wanted to turn the heating on manually in extreme conditions (for example i walk in at 2pm and the house is cold) whats the best way of doing that? Would that be to use the manual setting and just notch up the thermostat setting a few degrees?
Thanks again

We are retired so at home all day. The temperature is therefore constant. I have setting 1 to when we wake up and setting 6 to when we go to bed. Settings 2 to 5 are spread evenly throughout the day at the same temp as setting 1. If we feel the need to put the temperature up or down during the day we just use the up and down buttons (no need to use Manual). The temperature then stays at the new setting until the next time period, when it automatically reverts to the "standard" temperature.