Max. central heating water setpoint issue

[pbajdor]

I've been having some issues with my boiler recently. The CH maximum temperature setpoint setting appears stuck at 40°C and cannot be adjusted higher. When I try to decrease the temperature, it only goes down to 39°C- lower, never up. This seems to be a bug with the Viessmann 100W model. Initially, I found that the temperature was stuck at 55 (the same as the SAT temp) -> then I lowered it to 40->39st C. I found one forum where someone had the same. I've tried adjusting it through the SAT, OTGW, and even by connecting the Nest thermostat directly, but nothing works. I was informed that the motherboard might be faulty by Viessmann. Has anyone else experienced this issue?

[sergeantd83]

Was your boiler used to work correctly with SAT?

[pbajdor]

Well, it worked ok; it still heats the house. Initially, the 55C was set by the SAT.

[pbajdor]

I noticed the issue before the winter when I wanted to increase the CH temp.

[sergeantd83]

Do you have a knob in front of your boiler that needs to be turned clockwise that controls the CH max setpoint??

[pbajdor]

Unfortunately, it is Viessmann 100w, so no physical knob. The ch max setpoint cannot be changed in the boiler menu either - it seems to be locked for some reason. I had my Viessman specialist the other day and he did not know why it is locked. He spent 2 hours on the phone with the Viessmann support.

[sergeantd83]

That’s indeed a weird issue.