I had a Jabsco
that would sometimes lock up on discharge. Sometimes it would operate properly and sometimes it would just sit there and not empty while I pumped and pumped. There was no extraordinary pressure on the pump and it is not a blocked discharge or tank vent, I checked those first. This is the guest head
and the intermittent operation was very embarrassing. So I changed the manual pump out for the Jabsco electric
conversion and, guess what, same issue. Sometimes it pumps out and sometimes it doesn't. It seems to me like some kind of airlock or loss of prime but I can't figure out why. It draws water
fine and the discharge is plumbed from the pump down about 6 inches and then up to the tank about 4' above the bowl.
Any ideas anyone? Please no recommendations for switching it out. It should work and I just want to figure out why.