Dear Dave,
The RV water pump stays on when hooked up to city water even when the switch is off. Also, the pump “hums” when the unit is shut down. It’s not as loud when the pump is actually pumping water through the system—there’s just a hum. The only way to shut it off is by pulling the fuse. I’ve tried pulling the fuse and waiting a few minutes then putting the fuse back in. The pump shuts off, but in a few minutes the hum starts again. Thanks for any help. —Matt, 2007 Newmar Dutch Star 4304
Dear Matt,
If the water pump stays on when hooked to city water, it typically means your water pump check valve is defective or stuck, allowing the pressurized water from the city source to backflow through the pump into the fresh water tank. This would reduce pressure in the line at the pump and it would sense that it needs to run to provide on demand pressure.
The “gremlin” in this situation is, why does it run with the switch off? That should mean there is no 12-volt power going to the pump. Pulling the fuse removes the gremlin. Therefore, it could be one of two things: Either your switch is defective and not shutting off power, or, more likely, is there is another switch somewhere that is on?
Typically your rig will have three water pump switches: one at the monitor panel, one in the bathroom, and one outside in the service center so you can turn the pump on in each of those locations. If any of these switches are in the on or closed position, 12-volt power will go to the pump and make it run when it detects a pressure drop.
Troubleshooting tips
Make sure all the switches are in the off position. If the pump still runs, you most likely have a defective switch. Start with one switch and remove one of the lead wires. If the pump still runs, replace the wire and go to the next switch, remove the wire, and do the same for the third.
Does the water pump work as designed when not connected to a pressurized city water source?
I believe the hum you are hearing when the unit is shut down most likely is water backflowing through the pump and the blade spinning.
I would suggest removing the water pump and replacing the backflow valve and the filter.
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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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