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Old 22-06-2015, 20:06   #1
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Fresh water pump conundrum

A few months ago, we rebuilt our fresh water pump and redid some of the plumbing between the pump, the filter and the hot water heater.

1) Since shortly after the rebuild, the pump has been acting like the tanks are empty when the water is still several inches above the intake. First it will run a few extra beats after you turn the water off, then it won't shut off on its own. Not that I let that happen for very long before lunging for the circuit board.

2) More recently, the pump goes off every half hour (almost exactly), but we haven't been able to find a leak anywhere. Moreover, we have not noticed the water tanks emptying any faster, nor is water accumulating in the bilge any more than normal.

3) Finally, just in case it could be related, this weekend we noticed some engine coolant collecting on the rim of the hot water tank, presumably leaking from somewhere in the exchange set up, although we haven't been able to figure out where. With the water tank off, we haven't observed any new accumulation, even after we went to the pump out dock this morning.

Yep, I feel like an F in troubleshooting this week
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Old 22-06-2015, 20:27   #2
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Re: Fresh water pump conundrum

First I would not drink any of the hot water from the water heater until you find where the engine coolant is leaking.

Odd are there is a leak under the engine coolant hose clamp on the water heater and its not a problem, other then new hose. worst case there is a pinhole leak in the heat exchanger.

The water pump, might just have a worn plate or plunger bits, tight bearings, etc that keeps it from developing enough suction lift to pull the last bit of the water out of the tank. I assume the tank suction is below the pump inlet.

Might be time for a new water pump. and some heater hose.
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Old 23-06-2015, 04:09   #3
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Re: Fresh water pump conundrum

Is the pressure relief valve on the hot water tank leaking? I'm currently awaiting a replacement for mine. Only noticed mine when I hooked up the 240 volt element for the first time last week. Then I checked with motor running & sure enough was leaking also.

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Old 23-06-2015, 12:42   #4
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Re: Fresh water pump conundrum

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Originally Posted by gspeak View Post
Is the pressure relief valve on the hot water tank leaking? I'm currently awaiting a replacement for mine. Only noticed mine when I hooked up the 240 volt element for the first time last week. Then I checked with motor running & sure enough was leaking also.

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It didn't *seem* to be coming from there, but as we only went to the pump out dock, the water wasn't that hot. I am going to turn the AC heating element back on today and see if we notice anything.

It really doesn't seem to be coming from the hoses, but we cleaned up everything so that we can watch from now on.

As for needing a new pump, I am starting to see why people just get new instead of rebuilding in the first place. It seems like I always need new a few months later, anyway and rebuild kits for just about everything are a significant percentage of the replacement cost!
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Old 23-06-2015, 13:11   #5
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Re: Fresh water pump conundrum

What kind of pump is it? If jabsco positive displacement type. Could be the valves are not seated properly.
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Old 23-06-2015, 13:14   #6
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Re: Fresh water pump conundrum

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What kind of pump is it? If jabsco positive displacement type. Could be the valves are not seated properly.
It is Shurflo, but we will take it apart again before we replace it.
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Old 23-06-2015, 13:19   #7
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Re: Fresh water pump conundrum

Could be some air in the high point in your system... a loop of hose? I have also found that a very small drip (and I mean only one occasional drop) will make the pump cycle at night etc. ... especially if you don't have an accumulator.
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Old 24-06-2015, 14:48   #8
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Re: Fresh water pump conundrum

The pump problem you describe is often caused by water leaking back through the pump from the pressure side to the suction side. When enough water flows back toward the tank, the pressure drops and the pump runs. This cycle repeats at a very regular interval and no water is lost from the system.


Replace the valves or replace the pump.
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Old 25-06-2015, 08:23   #9
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Re: Fresh water pump conundrum

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The pump problem you describe is often caused by water leaking back through the pump from the pressure side to the suction side. When enough water flows back toward the tank, the pressure drops and the pump runs. This cycle repeats at a very regular interval and no water is lost from the system

Replace the valves or replace the pump.
Fresh Water Pressure Pumps
I agree with the above. Keeping things clean during re-build is important. cleaning the suction hose during reassembly will insure nothing came lose and got stuck in one of the valves. It doesn't take much to cause a back flow leak. Sure-flows are easy to rebuild. I've rebuilt many and the one I have now was rebuilt a year ago and is still runnin' good.

The water heater is another problem. Are you losing coolant level in the engine? If not it's likely a pin hole in the hot water exchanger, as the fresh water pressure is higher than coolant pressure. Is there a coolant overflow after long periods with engine not running and pressurizer freshwater. The above leak would still be evident. I wouldn't drink hot OR cold water, as the check valve betwixt them doesn't always seal completely. Coolant being in the hot water heater pan? There should be evidence of an external leak at the water heater. which if the above is the case you'll have two leaks. Good luck.
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Old 25-06-2015, 10:21   #10
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Re: Fresh water pump conundrum

Can the exchange on the hot water heater be replaced, if we determine that is the issue? We cannot see any external sign of leakage: it seems to be coming from underneath the white cladding. And yes, it is worst when the engine hasn't run.

I hope someone in town has a valve in stock, I had to order the rebuild kit online.
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Old 25-06-2015, 10:34   #11
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Re: Fresh water pump conundrum

Is it an adjustable pressure valve on the Shurflow pump? Mine has a screw in the center of the pressure valve that you need to adjust to set the correct pressure for your application.
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Old 25-06-2015, 17:24   #12
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Re: Fresh water pump conundrum

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Originally Posted by Greenhand View Post
Can the exchange on the hot water heater be replaced, if we determine that is the issue? We cannot see any external sign of leakage: it seems to be coming from underneath the white cladding. And yes, it is worst when the engine hasn't run.

I hope someone in town has a valve in stock, I had to order the rebuild kit online.
If the core in the hot water heater is leaking, no, replace the whole unit. from what you've just posted it probably is the core. you can test it by disconnecting the coolant hoses from it...the ones leading from the engine...and cap one and make a test adaptor for the other side with a PVC pipe and cap. drill a small hole in the cap and insert a shreader valve pump it up with a bicycle pump and see if it holds pressure for a couple hours. check your connections with soapy water, for leaks in your test connections. if it leaks replace the unit. if this is the case then the pressure water leak is solved. if not proceed to the following ;-)

if you've just installed the rebuild kit on a sure flow pump. just pull it apart and clean everything and put it back together. I don't believe you can buy individual parts. if you've damaged something in the previous rebuild, than a new kit is advised. In my experience, back flow is caused by small particles in one or more of the check valves....the little rubber discs on the front side of the head.

Hope this helped you.
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