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Water pump sucking air?

Jul 6, 2017
Hunter H 41DS Hampton, VA
This is a new problem for me. When I leave my boat overnight the water pressure in the freshwater system drops to nothing. When I turn on the water pump it clearly sounds like it is running dry. I have to open up a faucet and let it run for 30 seconds or so then the pump will pick up some water and pressurize the system. I can't see or find any leaks. I'm thinking perhaps there is an internal check valve in the pump that's leaking back into the tanks or something else????

Any ideas?
May 1, 2011
Pearson 37 Lusby MD
Do you have a small water filter in the line? I have one on my boat that I have to invert so it doesn't suck air.
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Dec 31, 2016
Beneteau Oceanis 351 Charlottetown
If you suspect a leak, food dye in your water tank will help locate it.
May 24, 2004
CC 30 South Florida
Sorry had misunderstood your question. Yes, your pump has a check valve and it could be stuck. Even if the pump is powered off, most of residual pressure should be maintained, especially from one day to the next. Not familiar with your boat and whether other check valves could be present. Before powering the pump On check each faucet to see if all loose pressure or just one. It could help determine if there are other check valves.
Dec 25, 2000
Hunter Passage 42 Shelter Bay, WA
Hi Tim, what happens if you pressurize the system, leave the pump on and shut off all faucets? Does the pump cycle periodically? If so, it is a faulty check valve. Easy to replace as I did mine. If not, something else is going on.
Jan 24, 2017
Hunter 34 Toms River Nj
Check o rings on pump connection
If it’s the newer type that is a compression o ring with a retainer clip, mine had double o rings that one failed and did the same thing
Jan 19, 2010
Catalina 34 Casco Bay
101 leak source school says to spray all connections with a soap solution. Do this first thing when your system is making up.. The air being pushed by the water will bubble at your leak(s)


Sep 28, 2008
Hunter 41DS Punta Gorda, FL
Tim, I had the same issue with our 41DS. It only happened with the Port water Tank. It would running fine but overnight it seemed like it would lose suction and just continue to run. It was bothersome to say the least. I changed the fitting on the tank and replaced the suction valve at the pump and have had no issues since. My gut feeling was that one of the fittings either on the valve or tank had just come loose enough to allow a little air in the system until the pump finally saw it. I bought the fittings from Freshwatersytems.com. The one at the tank was a metal fitting.