I have 20 rads, HR92 on all of them, alpha2-50/60 pump. viessman 26kw boiler. sealed system. Alpha pump needs to be set on PP3 mode for noise avoidance (Avoid the usual very noisy / resonance behaviour with when call for heat level is just 1 rad open a tiny bit). Due to a catastrophic leak in the ground-floor screed-buried CH piping when we went to sealed about 6 years back, there is a set of 4 ground floor rads that are on a really long and convoluted run from upstairs with drops from the ceiling inside cupboards etc. I've recently got into homeassistant/esphome monitoring of everything, temperature probes everywhere, and confirmed my suspicions , that particular group of 4 will not warm up in any reasonable time, if more than a couple of the other rads are on - the flow simply prefers not to go that way until its got no other options. but I can get the flow to go that way if I whack the pump up to speed III. which is not a long term solution due to the aforementioned noise ....

  1. if there is such a thing, find a pump that is by default variable speed like the alpha, but can be forced to go "max" with an external trigger input of some kind. doesn't need to be fully automated.. human button press is fine, but needs to revert to the variable setting once the trigger is unset.
  2. go up to alpha 2-80 pump, hoping that the increased head will help
  3. split the system with a LLH/buffer, putting the "slow" group on a separate pump to the rest. There'd then have be 3 pumps - one primary side, 2 secondary side. The slow group has T off point on the flow and return sides so perfectly do-able to re-plumb it. But how do I control multiple pumps from evohome? "if zones 3 and 7 calling for heat then power up relay X", doesn't exist as an output option.
  4. as previous but don't separate the pump controls - rely on alpha pump's standby mode to stop , if there is no open rad in that zone.
  5. spend a stupendous amount of time trying to "balance" - if that is even possible with evohome (read many recommendations to suggest that its not worth the effort)