Low flow setpoint short-cycling

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wintersteiger
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Joined: Mon May 01, 2023 1:14 pm

Low flow setpoint short-cycling

Post by wintersteiger »

This is clearly not an OTGW question, but I wonder whether someone in this forum could help my understand my boiler's behaviour. If there's a better suited forum for this kind of question, I'd be grateful for pointers!

The behaviour that I'm observing is that the boiler fires in irregular, short intervals when I set the flow setpoint to 5C, while both outside temperature and flow temperature are > 20C. Instead of turning it off altogether, I figured it would be fine to set it to a low setpoint, but apparently it doesn't like that. This is what it looks like:

low-temp-short-cycling.png
low-temp-short-cycling.png (212.54 KiB) Viewed 5481 times

There was no DHW activity during this time and the master-OTC bit was disabled (ID1:HB3=0). I've seen the same with OTC enabled just a few hours later though:

low-temp-short-cycling-otc.png
low-temp-short-cycling-otc.png (158.57 KiB) Viewed 5481 times

I have absolutely no idea why it would do that. "Master low-off" in the OpenTherm specification sounds related and I see ID3:HB4=0. Does that mean I'm not supposed to "go low" instead of turning CH off? The boiler also reports MaxTSet-LB = 30C (ID49:HB). Is this an attempt to tell me that it wants me to keep TSet > 30 (instead of MAX TSet)?

(Boiler is an Ideal Vogue Max Combi 32kW.)
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