Boiler cycling problem with CM Zone System

[PeterH]

I first posted on this forum over one year ago after problems with my new CM Zone system needlessly calling the boiler to cycle. Although I never solved this problem it seemed to become less noticeable so I forgot about it and hoped it had gone away.

My system comprises 2 CM 67zs, 6 HR80UKs (3 in one zone rest 1 per zone) and 1 HC60NG.

With the heating season back again, albeit with kinder weather so far, it's back with a vengance. The basic problem is that when the ambient temperature is slightly above the set temperature the boiler cycling comes on even through the rads stay fully shut and stone cold.

This seems to be worse because of the warmer weather because the ambient temperature hovers around the set point - when it's colder the heating has to come on full blast rather than cycling.

I have tried numerous different parameter settings but none make any difference. I've now resorted to setting the minimum on time to 1 minute (3:Ot=1) rather than the recommended 4 for my oil fired boiler, and cycle rate 3 per hour (8:Cr=3) so now it onely does it for 1 minute every 20 minutes. Still uses fuel to do nothing though.

My questions are: Will the minimum cycle time of 1 minute do my oil fired boiler any harm; and does anyone else have this cycling problem and has anyone any suggestions how to fix it - are there any other parameters that can be adjusted to stop this (eg what does the Proportional Band Width parameter do- is it anything to do with how close to the setpoint the controller thinks about calling for heat?) Of course Honeywell documentation completely useless about any of this but I've come to expect this as part of the normal service.

Any ideas would be gratefully received.

Peter

[MichaelD]

There is a thread on this elsewhere in the forum. My guess is that you may have a communications problem:

In the detailed instruction sheet for the CM67z, it has a parameter 16 which controls the actions if communications is lost.

"The CM67Z allows you to set the fail-safe mode of operation of the heating system if radio communication is lost. By default HC60 boiler controller relay will be switched OFF in case of communication loss. Alternatively you may choose to cycle the boiler at 2 min ON and 8min OFF. Useful when the building is not occupied for long periods of time and there is a high risk of frost damage."

I wonder if you have parameter 16 set to 1, which will give you 2 minutes on in every 10 minutes if you've lost a connection? Sounds like that might be what you're experiencing. If so, change parameter 16 to 0 and see if it makes a difference.

Let us know how you get on

Michael

[PeterH]

Hi, thanks for your reply. I started a thread on this over a year ago and have read all the various comments on this issue very carefully. Several people have suggested a communication problem but that's not it. The HC60 would show a red light if it did not receive a signal and had reverted to non-communication mode. Moreover the cycle times respond to having the parameters changed in the CM67z setup (ie cycles per hour and minimum on time) so the units are definitely talking to each other OK.

After many long discussions with Honeywell on this which got nowhere they finally hit me with the suggestion "this system is only designed for consumer use and you cannot expect it to be perfect", which I think is a completely unacceptable response. These are complex devices which are sold as a hightech control device for domestic installations and they should work properly. Having the boiler come on when the ambient temperature is steady and above the set temperature means the system does not do what it's supposed to do and therefore does not work properly, period.

In the absence of any other ideas I think the conclusion is that the CM Zone system is indeed badly designed, and badly supported by Honeywell. I just hope someone from Honeywell reads this and bothers to come back and try to do something about it.

[scocherry]

Hi, thanks for your reply. I started a thread on this over a year ago and have read all the various comments on this issue very carefully. Several people have suggested a communication problem but that's not it. The HC60 would show a red light if it did not receive a signal and had reverted to non-communication mode. Moreover the cycle times respond to having the parameters changed in the CM67z setup (ie cycles per hour and minimum on time) so the units are definitely talking to each other OK.

After many long discussions with Honeywell on this which got nowhere they finally hit me with the suggestion "this system is only designed for consumer use and you cannot expect it to be perfect", which I think is a completely unacceptable response. These are complex devices which are sold as a hightech control device for domestic installations and they should work properly. Having the boiler come on when the ambient temperature is steady and above the set temperature means the system does not do what it's supposed to do and therefore does not work properly, period.

In the absence of any other ideas I think the conclusion is that the CM Zone system is indeed badly designed, and badly supported by Honeywell. I just hope someone from Honeywell reads this and bothers to come back and try to do something about it.

Hi Peter et all.

I have recently installed a CM Zone system - well actually two kits put together. I have 12 HR80 in 3 zones, a HC60NG boiler relay and a HRC0NG zone valve relay and two CM67zs.

I seem to be getting the same problem as you with the HC60NG boiler relay cycling on for a couple of minutes when there is no demand. The HC60NG zone valve relay works fine, its only the HC60NG with the HR80s bound to it that has a problem.

Did you ever get a fix for this problem? Is it an HR80 sending a false signal to the HC60 or is it just the HC60 switching all by its self? It wouldn't be such a huge problem if the boiler wasn't next to my bedroom.

Any thoughts from anyone would be appreciated.

Regards
Scott

[PeterH]

Hi Scott. I haven't been on the forum for a while as I've basically given up hoping to find a fix to this. I forgot about it over the summer but now the heating's back on again it's annoying me once more!

So far as I've been able to understand the system is designed to cycle so long as the ambient temperature is within one degree (or something like that) of the set temperature. I suppose the logic of this is that the TRV is able to demand instant hot water whenever it needs it for a short time so as to keep the ambient temperature within the target band. The down side is that effectively you have to pay to keep your boiler at working temperature even when the heat is not needed. This wastes energy and money and while it may enable the temperature to be controlled more effectively I'm not convinced it's a good trade off against efficiency.

The system could be massively improved if the software was upgraded to allow cycling to be turned off when the ambient temperature is within a set range of the target temperature. Default can be left to run as it is but for those of us that want to we could enable this. Even better would be the possibility to set the range it applies to.

Hope Honeywell are listening!

Peter

[scocherry]

Hc60ng Cycling Boiler

Thanks Peter

That would make sense but mine is happening when all the HR80 are set to 5C i.e. off.

I think it will have to be a long journey of trial an error to see which HR80 is sending the signal if any!

Kind Regards
Scott

[JohnnyP]

Not sure I can help, but here are the two cases when my Hometronic setup has fired up the boiler when I didn't want it to: first, when the heating has reached, or is near equilibrium, the boiler is cycled to ensure quick response if a heat demand is received; second, when the controller, in my case HCM200d, has lost contact with one or more HR80s, in which case it enters a frost protect mode.

The first case is well documented on this forum and happens when your setpoints are near ambient temperatures. Doesn't sound like this is your case, unless you live somewhere very cold, around 5C!

The second case can be checked by actually looking at all of your HR80s when the condition occurs - if one of them displays 20C and no antenna symbol, then comms have been lost.

Neither really sounds like your problem, but worth ruling them out. Best of luck.

PS. A third possibility is that you really do live somewhere cold and the normal frost protect is kicking in.

[drawdog]

Solution

Below is part of another thread on this subject. Folks, don't beat yourselves up with this problem - just work around it as below. I'm into my second heating season with no cycling, it really works well.

The HC60NG has been cycling my boiler for some time now and slowly driving me crazy, so why I didn't think of this solution before now is a mistery !

I've added a 'time delay' relay into the boiler control circuit. The relay coil is energised by the HC60NG when calling for heating, the relay contacts supply the boiler with 240v. The relay allows a variable time delay to be set between the coil energising and the contacts closing. I've used 10min as a delay time.

If the HC60NG is simply cycling (as it tends to do, a lot) then the relay will receive the 240v feed, but the boiler will only start if the 240v feed exists for more than 10mins (in my case). As a result the relay filters out the cycling request and only starts the boiler when the controls are making a more serious request for heat.

Boiler cycling has now completely stopped, the only very minor downside is that I have to wait 10mins before the boiler will start after a genuine request but this has actually not been noticed