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I have a Glowworm Ultracom 30cxi fitted in the loft (out of sight out of mind) driven off a Honeywell CM921 wireless stat. With the cold weather I've taken more interest in it, and noticed that it's cycling a lot, and this seems to be because the boiler's often failing to modulate the burner.
For example, I've the CH temp set to 80 degrees. What often happens is that the burner comes on (3-4 flames on the display), the flow temp rises to 80 (from say 50 degrees, taking maybe 20-30 seconds), and then instead of the burner being modulated down (to 1-2 flames on the display) once it's reached target, it keeps it on high, so that the flow temp overshoots. It seems that when it's 2 degrees over the target temp (so 82 in this example), the burner cuts out fully, then the pump runs for N minutes, followed by a few seconds silence, before the whole thing is repeated again. This doesn't seem right!
Now it doesn't always do this. Sometime, as the target flow temp is reached, it correctly modulates the burner right down and maintains the flow at the target temp (or target-1 degree) without any problems.
I've not yet figured out the circumstances when it works properly and when it doesn't (boiler in the loft doesn't make it easy to watch it), to see if there's some pattern to things. I don't think I get the problem from cold though, as far as I can tell, it's seems to be more when the system has been on for a while (and maybe when the room temp is around the stat target temp - possibly, not sure about this) - I have had the problem when the room temp was a degree or two below the stat's target temp, so that stat should still have been calling for heat.
Anyone any ideas of what's happening?
I range rated the boiler down a bit (to 20kw, from default of 24) to see if this helped, but still got the problem.
cheers.
For example, I've the CH temp set to 80 degrees. What often happens is that the burner comes on (3-4 flames on the display), the flow temp rises to 80 (from say 50 degrees, taking maybe 20-30 seconds), and then instead of the burner being modulated down (to 1-2 flames on the display) once it's reached target, it keeps it on high, so that the flow temp overshoots. It seems that when it's 2 degrees over the target temp (so 82 in this example), the burner cuts out fully, then the pump runs for N minutes, followed by a few seconds silence, before the whole thing is repeated again. This doesn't seem right!
Now it doesn't always do this. Sometime, as the target flow temp is reached, it correctly modulates the burner right down and maintains the flow at the target temp (or target-1 degree) without any problems.
I've not yet figured out the circumstances when it works properly and when it doesn't (boiler in the loft doesn't make it easy to watch it), to see if there's some pattern to things. I don't think I get the problem from cold though, as far as I can tell, it's seems to be more when the system has been on for a while (and maybe when the room temp is around the stat target temp - possibly, not sure about this) - I have had the problem when the room temp was a degree or two below the stat's target temp, so that stat should still have been calling for heat.
Anyone any ideas of what's happening?
I range rated the boiler down a bit (to 20kw, from default of 24) to see if this helped, but still got the problem.
cheers.
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