I suspect there is at least a contributing issue with the volute/impeller being imperfect and causing cavitation and flow issues... I was told the pump seal had failed a while back (less than a year old) and the impeller was in bad shape and replaced as well at that time. I heard the impeller housing was not in great shape and getting the new impeller in was “tricky”. Obviously that’s not good..
If both units are cloned, swap the pumps and see if your issue transfers to the other boiler.
