The Stella-Z has four modes:
The Comfort and Energy Savings mode allow setpoint adjustment from 0 to 50 deg C.
Indigo doesn't have a direct correlation of its settings with the modes above AFAIK. It has a setting 'Heat On' which enables you to adjust the setpoint. Indigo doesn't support Direct Control which would give you direct control of the valve percentage opening but then temperature control is not handled by the Stella-Z.
My
Autolog Stella-Z Plugin controls the Stella-Z by setpoint adjustment - lowering the setpoint to 6 deg C (Frost) to turn the Stella-Z off. It is instantaneous as soon as the Stella-Z wakes up. You can also wake the Stella-Z manually by quickly pressing the button on the front.
I am currently working on an improved version of my plugin that is in beta testing and will be providing an updated Version 2 within a couple of weeks.