I have a problem with a Zoeller M53D pump. It worked fine even without the into 3/16" hole they advise you to drill in the 1-1/2” PVC vertical discharge pipe, which then pumps into a 1-1/2" PVC waste line. There is a combination check valve/union on this vertical discharge pipe. I also have a Home Guard backup unit which vertically discharges into it’s own 1-1/2” stack which then elbows over and tees into the same PVC pipe as the Zoeller, then onward into the main waste and out of the house.
After a year of this operation and setup, it started to "double fire"...the float would rise, trigger the pump which would cycle normally, then it sounded like water rushing back into the pit (down the discharge pipe?) whereby the pump would cycle again for a few seconds. I kept not getting to fix it, and now it is triple cycling…one main cycle followed by 2 more much shorter cycles, but all in a row.
First I took apart the union, drained the water from the pump and put it back together. This seemed to identify and remove a possible air lock as the problem as the pump went back to normal operation for at least a few hours. When I woke up the next morning, the pump was right back to triple cycling. I then took apart the union, drained the water and then finally drilled the 3/16” hole (pointing downward so the spray doesn’t go all over the place) in the vertical discharge pipe about 6-1/2” above where the PVC threads into the pump (as directed). Again the pump worked normally after this so I blamed an air lock on the problem. Within a few hours though the pump was back to triple cycling again!
I called Zoeller and spoke to them-they suggested it was either a faulty check valve OR a bad switch on the pump which could be easily replaced. I tend not to blame the switch since it worked fine after I took apart the union/check valve assembly. But why would the check valve then be to blame, if, again, everything did work for a short time after the union was undone???
I am going to separate and rerun the 2 PVC discharge lines for the Zoeller and the Home Guard and will see if there is any blockage. Next I would install a new union if the problem persists. Lastly I would mess with the switch or replace the whole pump. Does anyone have any other ideas on what to check next?