Honeywell CM67 strange behaviour!.

We've one of the above which is programmed to come on in the morning at

06:30 Hrs with a target temp of 21.0 deg c The previous night it turns down to 10 deg c at 22:30 hrs.

So I assume that it should hold, well not come on really!, the 10 deg till the next step in the morning when it cranks up to 21 ..

However its starting at 4 am with a target temp of 24 deg C clearly not desirable.

I've done a full reset in the installer menu to no avail. Anyone any ideas if theres something I've possibly overlooked, and yes its got a new set of duracell's ;)

Or is it time for a replacement?...

cheers..

Reply to
tony sayer
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Mine is doing something similar, turning on during the day when set back to 15 deg well in advance of the later target of 20.5. For the moment, I simply use the separate controller to disable daytime use, but it rather misses the point.

Chris

Reply to
Chris J Dixon

It sounds like you got the optimising turned on. I started off with this and on occasions found the heating switching on several hours early with the temp being just a couple of degrees below the target. I've now turned it off and just set the times a bit early to give a warming up period.

Reply to
Tony Bryer

Interesting, does anyone understand the algorithm which the optimisation is based on? I'd guess it should be fairly simple - it would measure the rate at which the system is usually able to raise the temperature, look at the gap between the prevailing temperature and the target and work out how early everything needs to come on. But for it to go this wrong it must be be trying to do something too clever for its own good? I've recently got the CM927, is this prone to the same problems?

Reply to
Martin Pentreath

Does optimising also increase the target temperature as Tony S reports? I don't think so. Tony S, have you tried mailing Honeywell? How old is the thermostat?

Thanks for this, I need to check what my CM907 does; trouble is I am either away or asleep when optimisation normally kicks in. Need to set up an experiment :-)

Kostas

Reply to
Kostas Kavoussanakis

It is presumably an adaptive process - hence it may take a number of iterations to arrive at appropriate settings.

Reply to
John Rumm

Could it be using the (low) setting of 10 degrees as part of its optimisation - even though the house will never get so cold - it may be planning to heat it from that temperature and therefore turns on early.

I suggest changing from 10 degrees to something more practical - such as 17 degrees and see what happens.

Reply to
John

Usually for temperature control, the method used is PID.

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the system applies 100% power for a period of time and measures the rate of rise, it usually requires a large span to calculate correctly. This may explain why it is doing it when your controller is setback. Once it has carried out several iterations, it will know the rate of rise, and can calculate start time accordingly. Obviously in this environment it is not true PID control.

Reply to
Vernon

Ah!, its intended with 21, not what it is doing..

Haven't mailed Honeywell yet thought peeps here would have err.. more experience;)

Reply to
tony sayer

In article , John scribeth thus

Good thinking .. I'll try that and see..

Thanks..

Reply to
tony sayer

Imagine the guy programming the logic of the device "Let's see, we need to raise the temp from the low setting to the next setting. We will use this difference to calculate the start time" Flawed logic maybe as it should perhaps be using the ACTUAL low temp rather than the low target temp, but perhaps there is a good reason.

Let us know the outcome. I have my thermostat set at 17 during the night and it rarely comes on (if it does then I am grateful!)

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Reply to
John

I just gave up on it. Truth be said, for me I may regard 21C as the comfortable temperature, I don't really worry if it's 18C when I come in if the temperature is rising.

Reply to
Tony Bryer

In article , John scribeth thus

Well seemed to be fine last nite with the new revised settings but then again it wasn't quite so cold as it has been!..

We'll keep it under review for the time being.. Mind you the new wireless one would make the positioning of it better;!...

Reply to
tony sayer

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