I have some heating zones which run off a Grundfos Alpha pump which is set to the "auto" mode.
Heating seems to work fine - rooms heat up normally and this doesn't seem to take an unusually long time.
However I noticed that when the pump is on and shows power usage, it also shows 0 flow. That doesn't seem to make sense.
The various runs to the heaters are between approx. 20-40' one-way distances through 1/2" EVOH PEX. There is a zone valve for each loop and the shared pump is triggered on/off by a controller (Taco).
There is no appreciable noise when it is running.
I switched it out of "auto" mode as a test, and then it does show 1 GPM of flow:
which still seems really small?
I know the alpha is supposed to be efficient, but how to reconcile almost-no-flow with heating working OK?
I don't have any other direct way of measuring flow rate.
(So it does go to 0 in the 'alpha' range, but that doesn't tell me much... AFAIK any centrifugal pump could spin, consume power, and move no water; but that doesn't seem to be the case here.)