I spent/wasted an hour in my workshop today, trying to pull apart and investigate, the Grundfos Alpha+ circulation pump. I fitted a new replacement pump, on Monday, to get the heating system back online...
Powering it up, it was completely dead. I got the main water casing off, checked the impeller, bearings, all fine. then attempted to get to the pcb, for the variable speed. I managed to get half the electronics cover off, but that only gave access to the back of the pcb - I could not find an easy way, to release the pcb, to investigate further, though all looked fine.