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Old 09-28-2021, 09:59 AM   #1
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Fresh Water Pump

My fresh water pump has recently started cycling when no water is being used. It's most noiceable when sleeping. Probably about every 15-20 minutes it will run for a couple seconds. I see no signs of leaks anywhere. I'm thinking it's the pump itself maybe losing pressure through the check valve or something like that. For troubleshooting, I'm thinking if I pressurize the system then turn off the valve at the entry to the water pump, that may prevent it from losing pressure. If it doesn't turn on for an hour, it would indicate the pump being the problem. Any thoughts? Anyone have a similar issue?
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Old 09-28-2021, 10:01 AM   #2
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My washdown pump leaks back slightly through the pump as you're describing. Valving off the pump inlet and confirming whether or not pressure holds would be a good test for if the leak is internal to the pump or elsewhere.
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Old 09-28-2021, 10:06 AM   #3
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Originally Posted by backinblue View Post
My fresh water pump has recently started cycling when no water is being used. It's most noiceable when sleeping. Probably about every 15-20 minutes it will run for a couple seconds. I see no signs of leaks anywhere. I'm thinking it's the pump itself maybe losing pressure through the check valve or something like that. For troubleshooting, I'm thinking if I pressurize the system then turn off the valve at the entry to the water pump, that may prevent it from losing pressure. If it doesn't turn on for an hour, it would indicate the pump being the problem. Any thoughts? Anyone have a similar issue?
Do you have an accumulator tank? If so, try adding a little air pressure to it, through the Schrader valve on the top. Doesn't need much, but if depleted, could cause the cycling you describe.
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Old 09-28-2021, 10:06 AM   #4
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My washdown pump leaks back slightly through the pump as you're describing. Valving off the pump inlet and confirming whether or not pressure holds would be a good test for if the leak is internal to the pump or elsewhere.
Thanks, I will try that next time I am on the boat for a while or overnight.
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Old 09-28-2021, 10:07 AM   #5
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Do you have an accumulator tank? If so, try adding a little air pressure to it, through the Schrader valve on the top. Doesn't need much, but if depleted, could cause the cycling you describe.
Thanks, but there is no accumulator tank.
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Old 09-28-2021, 10:23 AM   #6
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Pump cycles due to loss of water pressure. the pressure drops because the water is going somewhere. If no leaks are readily visible, your diagnostic approach listed is sound. If it keeps cycling, it may be the valve at the tank you close is leaking, or a very small leak in the system you are missing. even a small drip will cause the pump to cycle eventually.
Loss of charge in the expansion tank wont cause the cycling when water flow is stopped, the expansion tank reduces cycling when water is running, and helps prevent over pressurization of the fresh water system when the water heater heats up a cold tank of water and causes thermal expansion.
You are on the right track.
let us know what you find!
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Old 09-28-2021, 11:10 AM   #7
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You may just need to do a slight adjustment on the pressure switch as well...
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Old 09-28-2021, 09:47 PM   #8
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I was able to find a bad check valve by using a stethoscope to listen to it. You can hear the water running thru the valve. You can get one at many auto parts stores. Not very expensive.
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Old 09-28-2021, 10:26 PM   #9
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Blacknblue I think you are on the right track and your test should confirm it. I like Russell’s idea of a stethoscope as well.
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Old 09-28-2021, 10:47 PM   #10
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We had a motorhome with a water pump that would cycle during the night with no demand. After they had replaced the pump 3 times and I kept telling them it wasn’t the pump they finally found a ball valve that was worn and letting water backflow into the water tank. So yes, it can be a valve slowly leaking back to the tank. Hadn’t thought of the stethoscope to find the leak, good idea.
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Old 09-29-2021, 06:45 AM   #11
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Thanks for everyone's help, I'll try to get there today to do some more troubleshooting.
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Old 09-29-2021, 10:24 AM   #12
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On our boat, we turn off the breaker to the water pump before we retire.
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Old 09-29-2021, 10:25 AM   #13
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On our boat, we turn off the breaker to the water pump before we retire.
That's one way to deal with it, but then there would be no water to the toilet.
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