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.