Honeywell cm921 thermostat

[brute03]

Hi, we recently had a new boiler fitted with the Honeywell cm921. My old boiler was a back boilerwhere I could just programme it to come on at 6am and off at 7am and same thing for the evening.

when they programmed the honeyell they set the heating to come on at 6.30am 21° and to go off at 7am at12° and for the evening to come on at 6pm at 21° and off at at 8pm at 12°. The problem I have is that on the evening programme I checked the radiators at 7.20pm and the radiators were almost cold. Can anyone tell me why please?

All I want my heating to do is come on at the relevent times and keep the same heat in the radiators right the way through the programme and then switch off at the relevent time. Can I do this without the radiators going cold before the end time.

thanks in advance

 

[D_Hailsham]

When they programmed the Honeywell they set the heating to come on at 6.30am 21° and to go off at 7am at12° and for the evening to come on at 6pm at 21° and off at at 8pm at 12°.

That's only three hours heating a day! One hour in the morning, ok, you are going to work. But only two hours in the evening? Do you really go to bed so early?

The problem I have is that on the evening programme I checked the radiators at 7.20pm and the radiators were almost cold.

The important thing is: was the room maintaining the temperature set on the CM921? If it was, and the property is well insulated, the radiators could quite easily cool down until the room temperature has dropped enough for the room stat to turn the boiler on.

 

[Charnwood]

The rads could be cold because the room is up to temperature.

Does the room temperature feel comfortable at 7:20 with the rads cold?

 

[brute03]

To be honest ever since we had an overpayment with our provider, because the back boiler was bad it has made me very cautious of what we spend on gas. It did feel a little cold in the rooms last night. I am not very clued up on the old thermostat thing, and thought when we had everything installed I could just do the same thing like i did with the old system.

this could be a really stupid question, but can you turn the thermostat off on these devices, so I can just have the radiators on for the times stated and then cool down at the finishing time.

My worry is that because the setting is on auto I don't want the heating coming on in the middle of the night when we dont really need it.when we went to bed at 10.30pm the heating came on again. On my programme it should come on at 6pm and finish at 8pm.

 

[MrTherm]

It's no wonder the rads are cold - you have the temp set for 12 degrees 'off' - - ???

make sure the time block periods cover the temp setting with no overlap difference otherwise the low temp setting on the following block will enable. There a six time blocks on the Honeywell cm921 if i recall correctly.
All is explained in the users instructions.

 

[Steelmasons]

Move the slider to manual (will be on auto) and turn on/off to suit.

 

[brute03]

So on the off time would you say I would have the temp on say 21°? Do you know why it started heating up at 10.30pm again though?

 

[MrTherm]

Because that 10.30pm on period is not your last time block. Disable any middle blocks you do not need, example: have *block 1* as you start period and *block 6* last time period.

 

[brute03]

A, thats great thanks for all the help, im sure I will be back soon

 

[MrTherm]

If you should need the user guide ->

www.honeywelluk.com/Documents/User-Guide/pdf/1068.pdf

Good luck.

 

[Charnwood]

OP, you keep saying 'off', but in effect there are no on/offs with the 921, there are 6 time/temperature periods available over the 24 hours.
The 921 switches from one time/temperature period at the allotted time.

I wish we still had our CMT907. The landlord fitted a separate danfoss timer and stat which is a BOS in comparison, nowhere near as versatile.

My heating is currently on, the set temperature is 20°c, the flat is comfortable, the rads are cold.

Do you have any rads fitted with TRVs?

 

[MrTherm]

The time blocks of the cm921 are very flexible, here is one method to equivalate to brute03's old boiler setting of 6am until 7am morning and 6pm until 7pm evenings.

Set period 1 to start 6am 'active' at say 21 degrees. (this will run until period 2)

Set period 2 to start 7am 'active' at say 5 degrees. (won't come on)

Set periods 3 and 4 to 'disabled'

Set period 5 to start 6pm 'active' at say 21 degrees. (this will run until period 6)

set period 6 to start 7pm 'active at say 5 degrees. (won't come on)

Suggest to try this setting initially just to get the feel of the old boiler timings.