Fresh water pump

Mar 3, 2008
Hunter 356 Lake Stockton
When we opened the boat to start the season last week, we noticed that the water pump was cycling every 15 seconds or so just as if we had left a faucet dripping or had a leak. After determining that all faucets were tight and no leaks appeared, we think our 14-year old Jabsco Parmax 31395 pump needs replacing. Any other thoughts before we order a new pump? Thank you for your comments.
Oct 3, 2014
Hunter 33.5 & Lake City, MN
Perhaps you have an air leak?

I would test the system like this:

First, wait for the pump to run. As soon as it shuts off, turn off power to the pump (to prevent it from turning back on during testing). Open a faucet right away and observe the water pressure.

Turn the power back on, wait for the pump to run, then turn off the power to the pump as soon as it quits. Wait 15 seconds (or so...time the pump cycle to be sure) and open the same faucet. Observe the water pressure. Is it considerably less? Is it the same? If less, then the pump is probably doing it's job and a new pump won't solve the problem. The problem is maintaining pressure (indicating a leak of some sort), not creating pressure (indicating a pump problem).

So now you have a visual baseline for the pump cycle at high pressure (immediately after the pump stops) and low pressure (when it would normally turn on).

Now let the pump run but wait 60 seconds, then 120 seconds before testing the pressure. What's happening? If the pressure further decreases as the time increases between shut off and pressure test, that would confirm that there is a leak somewhere.
May 24, 2004
CC 30 South Florida
I have a simpler test for the pump. Disconnect the output line from the pump and connect a piece of hose. Turn the pump on and allow all air to be purged from the hose and then stop flow with your thumb. The pump should cycle off and remain off for at least 2-3 minutes. Remove your thumb and the pump should turn on. If the pump passes the test then there is a leak in the system but if it fails the test then replace. The pump is obviously operating but it is the pressure switch that could be bad. If you determine there is a leak in the system starting at the pump check all lines and connections, check all fixtures, the water heater exchanger, transom shower, etc. I find that sometimes isolating or by-passing one plumbing circuit at a time may quickly point to the culprit. A 15 second cycle would indicate the presence of a rather significant leak which should be easily spotted.
Dec 25, 2000
Hunter Passage 42 Shelter Bay, WA
Ours was a different brand than yours, but it turned out to be a leaking check valve. Inexpensive and easy to replace rather than a new pump.
Dec 25, 2000
Hunter Passage 42 Shelter Bay, WA
Where is the check valve?
Hi Doug, the check valve on our model (Flojet) fresh water pump is one way with a design that prevents water from back flowing. Over time the check valve will gradually lose its ability to prevent back flowing, thus the pump cycling every few seconds. The Flojet check valve looks like this:

Also here in this PDF diagram, item #3:

Of course the first thing to check is to make sure there are no leaks in the plumbing. After that, I called the technical support center, gave them the symptoms and that is what they told me was the likely culprit. They do just wear out, in this case about ten years. Very easy to replace with simple tools.

When we took possession in 2002 the PO had tried different repairs; one was the pressure switch. I did find a leak in the system, at a fitting, in what was an awful location. Repaired that fitting, but the cycling persisted, albeit less frequently. System has been leak free now for few years and of course no cycling.
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Jan 12, 2011
Hunter 410 full time cruiser
My pump got to the point or running every couple of hours at night. I finally replaced it with my spare as I was sure it was the pump leaking back. The old pump is now the spare, every cruiser should have a spare pump.
Feb 8, 2014
Columbia 36 Muskegon
If there's a leak, the water has to be going somewhere. If your bilge is normally dry, it's a no brainer, fresh water in the bilge would be a give away. If normally wet, it's a lot harder to track down.
The idea of blocking the outlet and running the pump is a good one. If the pump still cycles the leak is internal. If it holds pressure the leak is elsewhere
Mar 20, 2004
Hunter 356 and 216 Portland, ME
Hi Doug and Karen!
All of the above comments are good, but a hidden leak is also a possibility. At the end of last season I had a similar problem; after much hunting, it turned out to be a leak in the worst possible place on a 356. It was the hot water line to the head shower - I just turned that line off on the manifold and now I'm working on fixing it. The hot water line, cold water line, and the head sink lines run from the manifold across the boat, under the nav station and turns aft under the forward head bulkhead. right at the turn the hot water line wedged between the hull and the edge of the bulkhead - there's a small gap - and over the years chafed a small hole. the hole is big enough to cycle the pump but not big enough for the water to be obvious in the bilge. I can only see the leak with an inspection camera. I'm trying to use the old line to pull a replacement through, but until then we shower on the stern - or ashore


Jan 20, 2005
Nauticat 321 pilothouse 32 Erie PA
call par jabsco. many of their pumps have rebuild kits that are usable to save the cost of a new pump. (it's like lego for grownups.) i just saved a 380$ par jabsco belt drive bilge pump from the dumpster with a $50 rebuild kit...