pressured water pump pulsing

woodster · Jul 4, 2014

do you have a pressure accumulator in the system

Bad Obsession · Jul 4, 2014

I am not sure about this. If you system is pulsing every 15 seconds the water has to be going somewhere. Have you tried draining your bilge dry and then checking it later on to see if it is fresh water in the bilge? There has to be a place for the water to go if it is leaking.

Not sure how big your system is, but I often toyed with the idea of taking the fresh water lines and replacing them.

Also, check the strainer that should be in the line before the pump. That could be a source of a leak.

capejt · Jul 4, 2014

Air-Lock? (a bubble in the system)

Stu Jackson · Jul 4, 2014

Water doesn't have to be coming out to have a small enough leak to cycle the pump. Tighten all the hose clamps. If that doesn't work, then either there's a leaking hose somewhere along the length NOT at a joint or the pressure sensor at the pump is faulty, but this is pretty rare.

I had that issue last June, and I replaced all the hoses which fixed the issue. Heck, after 27 years, the hoses did need to be replaced. Found the little leak halfway along a 20 foot length under the engine between the galley sink and the head sink. No way to be able to see it. The leak was so small that water never accumulated, but it was enough to cycle the pump.

You can check whether it's the pressure switch by simply disconnecting the output of the pump, putting a short length of hose on it and clamping it shut. If the pump works fine when it's on with this short hose, then you do have a leak somewhere.

Oh, and it's covered in the troubleshooting guide in the pump manual.

RTFM, F stands for funny.

shemandr · Jul 4, 2014

Isn't the pump supposed to cycle on to test if there is pressure in the system? How long does it run for?
Could there be an air leak? For instance if air is leaking out of the hot water tank that could depressurize the system and allow the pump to cycle on.
That's all I've got.

Stu Jackson · Jul 4, 2014

Yes, the leak could be on either side of the pump. Try them both. But it's rarer to have one on the intake side, 'cuz it's not under pressure.

Ralph Johnstone · Jul 4, 2014

galynd said:
I've checked everything. The bilge is bone dry. Strainer is dry.

Pump discharge check valve leaking

Skipper · Jul 4, 2014

galynd said:
My jabsco fresh water pump pulses approximately every 15 seconds. The obvious answer is there is a leak somewhere in the lines/fittings/etc. However, I find no water accumulation, the bilge is dry. I've checked every line and connection, the hot water heater, both tanks.... everything. Is it possible the pressure switch on the pump is getting bad or perhaps the impeller on the pump is giving way? Thanks, Greg.

I had this issue with a diaphragm FW pump, except it was a constant on-and-off cycling till pressure fully built. Turned out to be the check valve at the back of the pump clogged. There's probably also a check valve in your water heater FW intake line. If either of these check valves are clogged (or more likely stuck), water slowly gets by to build pressure, hence the cycling.

Does the cycling ever stop if you just let it continue on?

jibes138 · Jul 4, 2014

I had this issue and it was the check valve in the pump. Apparently I never winterized it well enough and I think freezing conditions damaged it. A new pump worked great. You can probably get the parts and rebuild it but a new pump is probably not much more than the parts. A pump is around a hundred bucks but they last for years if properly maintained so maybe 10 bucks a year.

tommays · Jul 4, 2014

Most likely would be the check valve on the discharge port

thinwater · Jul 4, 2014

^^ What Tommays said, plus you need an accumulator (looks like a small propane tank with bladder in it). With a tiny back-leak and no accumulator, it's going to cycle.

SoSound · Jul 4, 2014

FWIW, I went through the same process on our 1990 F285. Replaced all of the water supply lines, the intake from the fresh water tank to the pump... Everything that I replaced improved the situation, but nothing completely solved the problem. Finally last summer 10 days into our two week trip, we accidentally ran the fresh water completely dry. After refilling, the pump WOULD NOT prime. We tried on and off for a couple of hours before letting it sit overnight. Just before making a phone call to see if someone could meet us at our next destination with a new pump, I tried again and it worked!

Before our next overnight, I bought a new pump and replaced it. Worked like a champ! No more cycling, and it primed much more quickly.

Ask yourself if you can trust it. Replacing it, or at least carrying a spare pump would not be a bad idea.

Bill Murray · Jul 5, 2014

if you have one, check the inlet for the city water on the outside (stern?) of the boat. I had this happen once and this was slightly loose - dripping leak on OUTSIDE of hull so no water accumulation inside boat....... If so, replace the washer and tighten

Steve Dion · Jul 5, 2014

Stern shower hoses get bent and leak too.

Chris Patterson · Jul 13, 2014

Take the line loose at either the tank or the pump and block it off. On the other end put a threaded shraeder valve And pressurize it with a small hand type bicycle pump. Then if there is a leak, it will be evident.

I don't think that is your problem though, but it will settle the question of intake side leaks..

BobM · Jul 13, 2014

Sounds like a blocked vent.

kloudie1 · Jul 14, 2014

A piece of debris in the pump discharge check valve.. Disassemble the cap of the pump and clean it out.. You may have some other problem on the suction side, but for the pressure valve to repeatedly call for pressure, the pressure in discharge has to be going somewhere.. if not a leak, then the check valve is letting pressure back to suction side.

pressured water pump pulsing

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