Here is a thread with this same issue on another forum, looks like WB have an issue with these boilers….
https://forum.buildhub.org.uk/topic/46179-worcester-bosch-greenstar-8000-system-boiler-issues/
I thought the Tado sent a switched live to a motorised valve which then opens and sends a switched live to the boiler and pump. If so how will the relay help?
I have experienced with these types of smart thermostats that setting the setback temp no more than 2c below set temp is more comfortable and ensures a reasonable heat up time.
This only happens if "comfort mode" is turned on. IME it doesnt work very well if the room temperature drops more than a couple of degrees below the next set temperature.
My mistake, further investigations reveal that on the Greenstar there is no manual procedure on the diverted valve and the boiler relies on an automatic air purge mode.