How to set night preset temperature?

[denpamusic]

Initially asked by @jszkiela72 here: denpamusic/PyPlumIO#19 (comment)

1. I have another boiler (Vaillant) integrated with HA in which I can set
   the day and night temperatures. In your integration, I can only set the
   temperature that is currently compatible with the schedule. Is there any
   way to set both temperatures?

[denpamusic]

Due to the way Plum's schedule works, there's way to set schedule temperature offset by changing heating_schedule_parameter via plum_ecomax.set_parameter service. For example setting this parameter to 10 will lower a temperature at night by 10 degrees Celsius. (If at day it set to 50, then at night it will be 40).

However if there's enough interest, I'll consider adding night temperature in UI as well, so we'll just treat this as a makeshift feature request.

But as you're currently experiencing other issues with schedules, I don't really expect it to work for the EM860P6-O until we figured it out, since setting this parameter also uses FrameType.REQUEST_SET_SCHEDULE which doesn't seem to work for your model: denpamusic/PyPlumIO#18