Vitodens boiler no longer firing at the lowest rate?

Steve Ebels_3

I'd hazard a guess that the increase in return temp is a result of the added insulation. Fewer BTU's are being "dropped off the train" out in the zone(s) so you would have a corresponding increase in return temp. The only variable you have to play with is the flow rate to get your Temp differential back up. This of course will not make the boiler cycle less often.

AFA the minimum firing rate goes, I'm not aware that it can be changed but I'd have to check the manuals to be sure.

Dan Miller_2

Compared to prior heating seasons, it appears that my vitodens 200 8-32 is either producing hotter water on the lowest firing rate, or else the boiler is no longer modulating to the lowest firing rate. The boiler used to heat the return water about 8C above (38C on a return of 30C) but now I'm getting 10C above (40C on a return of 30C) even if the setpoint was calling for less. The "humm" of the boiler also seems not as low as it used to be. While the system still works, the end result is that the boiler cycles more often. I know there are adjustments that can be made to the poti to limit the maximum output but I'm not aware of anything that would limit the minimum input? The only changes that have occured since last season were to have the boiler serviced and adding some insulation to the house, neither of which should have any effect on the firing rate (unless we think a cleaner heat exchanger can produce more heat?) Is there a way to find out at what firing rate the boiler is operating short of clocking the gas meter? Thanks.