Water pump runs when not using water

I had this problem and replaced the check valve to cure it. It was a cheap part and a quick repair. The most time was spent removing and reinstalling the pump.

OK, thanks. I didn't think of the pump itself allowing backflow to the tank. That makes sense. I will try running a full tank of water to see if that helps. It does seem that at times the pump doesn't cycle or very rarely cycles without water being used...so maybe the "check valve" is allowing some backflow at times due to debris being trapped.

It's leaking somewhere or the pump is leaking internally back to the tank. It only takes a very slow drip. My sons FW was leaking very slightly at the low point drains and the pressure side of the pump dump valve. I replaced the o rings in all three valves and problem solved. I have run his pump then shut it off and turned it on a week later and it didn't cycle.

A leak or the check valve

It could be an internal leak in the pump. It is sometimes caused by debris being trapped in the pressure valve. It sometimes can be cleared out by running a whole tank of water thru pump with faucets open. We are having the same problem with ours and our mobile rv tech guy gave us this explanation because we couldn't find any leaks either. Good luck!