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Old 28-09-2020, 15:51   #1
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Clogged fresh water system

I recently bought a used older boat. The fresh water system pump has seemed a bit sluggish lately. This morning one tank was dry and when I switched tanks still nothing. The pump runs for quite a while before stopping. But when the faucet it opened, some water comes out, a burst, then a trickle, then nothing. The source pipe has a T which goes to the manual foot pump and the electric pump. The foot pump is pumping water but the electric is behaving as described above. The boat has 2 water tanks and regardless which one is selected, the behavior is the same. I filled both tanks today and so it is not a matter of an empty tank. When I remove the source line from the electric pump there is a trickle for a few seconds then nothing. The same for the foot pump source line. I can suck on the open hose and get a mouthful of water but it takes a fair amount of suction. I have spent the day today trying to figure out where the problem is. It appears that it is upstream of the pumps but there is no valve to open upstream to check for water. Are there any suggestions of what steps should be taken next?
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Old 28-09-2020, 16:47   #2
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Re: Clogged fresh water system

Clogged in-line filter? Next guess...
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Old 28-09-2020, 16:50   #3
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Re: Clogged fresh water system

There is no inline filter. I suspect the master valve but it is a pvc pipe so taking it apart requires use of a hacksaw.
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Old 29-09-2020, 02:32   #4
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Re: Clogged fresh water system

My guess from experience is that the clogging is calcium deposits from hard water. You need a filter before the pump as it may well trash the FW pump. I clean our filter abouth monthly and get about a tablespoon of calcium flakes. The pump indicates there is a build up by taking longer and longer to get back to shut off after drawing water.
Shut off the tanks, remove the pump and investigate. Likely the pump is full of it. Fit a filter. If the lines are clogged, blow them out with a dinghy pump. When you refit with a filter, be prepared to empty the filter repeatedly until the backlog of crud has gone, and then regularly thereafter.
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Old 29-09-2020, 04:52   #5
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Re: Clogged fresh water system

"I can suck on the open hose and get a mouthful of water"

I'm glad that you didn't get a mouthful of dead mouse.

Calcium is one blockage, and perhaps likely, but there could be others. If it's one blockage, you know that it is closer to the tank than the junction between the two source tubes. I suggest that you take the cap off the tank and then blow it out backwards, probably with an air hose and a rag to partially keep the pressurized air in the hose and tank. Whatever is blocking the hose is lodged against the other side, so blowing it backwards should dislodge it, including calcium.

PVC has the wonderfully helpful property that as long as you leave a lip on both sides of a cut, you can very easily repair your cut with a connecting ring, even when it's hard to reach. I suggest you go boldly where others have not trod and find your problem blockage. Good luck with it.
Never let anything mechanical know that you are in a hurry.
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Old 29-09-2020, 13:11   #6
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Re: Clogged fresh water system

From those symptoms I'd put my money on an air-lock at the pressure pump. Note that the same thing happens to my system during spring commissioning or when I accidentally let the tank get empty. Good reason to not let that happen. To help resolve that issue, I installed a drain valve and a short hose at the pump outlet and I use this to release the air trapped in the water pump impeller. The pump is trying to pump air and it can't build enough pressure to clear the pipes. So far I've been able to resolve the issue when it happens.
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