Originally Posted by curmugeon
I have a 2015 Interstate Grand Tour (about 3 weeks old). On three occasions, I have parked the RV in a barn and come back a few days later to find the water pump running. The fresh water tank is about half full and the RV is on level ground. I shut the pump off and run the kitchen faucet until the line is empty. There is not much pressure behind the water coming out of the kitchen faucet. I then turn the pump on and let it run until the lime pressurizes and the pump turns off and there is strong pressure behind the water coming from the faucet. Also there is air in the line initially until the water flow clears the line.
What would cause the pump to start running for days and not pressurize the line?
How much wear and tear can the pump withstand running (dry?) before failing to produce pressure?
It's a diaphragm pump, and can run dry for a long time without being damaged, unlike an impeller pump. The most likely damage— if any— would be due to it overheating; most pumps are cooled by the water they pump. So if it still runs, you're good.
The pump is supposed to be self-priming, and from what you wrote, it appears to be priming properly because you do get some
flow when you open a faucet.
So my guess is that the check valve that keeps water from flowing backwards into the tank is not working properly. So what happens is, the pump activates from the loss of pressure and self-primes— or tries to. but with no faucets open, it compresses a bubble of air as soon as the pump primes. Most likely place for that bubble is the water heater. Try manually opening the pressure relief valve on the water heater to "burp" the heater, and see if that helps. But make sure the water heater is turned off and allowed to cool first— no need to scald yourself.