Mayfair bilge pump problem

[TiredOfWorking]

I have a bilge pump problem that has been driving me nuts for years. I have explained it to two different dealerships, and they look at me like I am from another planet. I have a Mayfair (Johnson) 500 GPH cartridge bilge pump mounted in the bottom of my Lund 1675 Explorer. This is the boat’s original configuration. I also have a water sensing switch installed so it will run automatically. When the boat was about a year old, I started having problems with the pump. The pump will run, but will not pump water. I have replaced the cartridge. I have replaced the entire pump. It seems to have some sort of air lock. I have found that if the pump is completely submerged, and I crack the top open a tiny amount while it is running, water will flood in from the top and it will start pumping water. Once it has started pumping water, it will work fine for days until it dries out completely. The drain hose looks fine. I don’t see any problems or restrictions. Any ideas?

[marine_man]

Have you tried running it with the outlet hose off, to isolate the pump vs the boat plumbing?

Definintely a problem I haven't heard of often...

marine_man

[TiredOfWorking]

Good idea. I'll try that. Thanks for the reply.