freshwater pump maddening problem

[BillHoughton]

The freshwater pump in our RV (2007 Itasca Navion) stopped holding pressure - it would run up to pressure, stop, then cycle every 15-20 seconds (estimated; never timed on the old pump). Based on advice here and at Winnebago, I bought a new pump and installed it; the problem recurred.

A very helpful customer service guy at Winnebago told me how to pressure test the system and stated that, if the system held pressure, the pump was defective. It held 90 pounds of air pressure for four minutes, so I ordered a second pump on the assumption that the first one was defective.

Same (bad word) problem with the newest pump, even after I ran all the fixtures to get the air out of the lines. Checked all kinds of stuff: opened water heater pressure relief valve in case there was air trapped (no), tested the check valve on the inlet to the water tank; removed the kitchen sink faucet aerator to confirm that I was getting water with no air in it; and so on.

A tech at Pentair/Shurflo, the pump manufacturer, suggests that I fiddle with the check valve setting, which I'll do tomorrow.

Another tech at Winnebago told the tech I've been working with that the check valve in the water heater could be seeping internally and creating the problem, although I don't see how that would make a difference (in a closed, pressurized system, pressure is equal everywhere). I can replace it without taking out the water heater, but I'd have to drain the water tanks (fresh water, water heater) and blow out the lines to avoid dripping on electronic parts (smart move, Winnebago!); but, again, I can't understand how it would make a difference.

Any other thoughts?

[BillHoughton]

I have now been through two Shurflo pumps with the same problem. The literature to which TC Bear linked was helpful, but even more helpful was talking with one of the customer service folks at Pentair/Shurflo, who walked me through an adjustment that lowers the shutoff point. This didn't fix the problem. When I talked with him today, he said that, yes, there's a known problem with the check valve on these pumps, and I should send it back and get another one.

Frustrating. Is there a pump manufacturer I should be considering instead of Pentair/Shurflo? I looked online, and a pump that was recommended as "best choice" seems to have the same problem.

Is it feasible to install a check valve upstream from the pump and not rely on the pump's check valve?

[Ray_IN]

No, not IMO.  an external check valve cannot compensate for the internal check valve in the  pump head.   I would do as stated, return it to the mfgr. for replacement. In the meantime buy a new one from Amazon and try it, their liberal return policy means you  can get your money back later.

[Lumpty]

Turn the bypass valves to the water heater to take that out of the pressurized part of the system. If the pump holds pressure then, it is something with the water heater.

[bobndot]

If u have an outside shower shut off the handles not just the shower head.
Check ur ice maker if u have one.
Dirt in the check valve or put a check valve on the inlet side to prevent the pressure relieving back up the line ?

[enblethen]

Another item to check for a water leak is the pressure relief valve.
heck the low point drains.

[bobndot]

Imo , something is leaking. Check the drain on the water heater to be sure its tight.
Check all plastic valves, like bypass valves, rear of toilet valve.

[TCBear]

I have no idea if this could be your problem, but from the Shurflo manual: "The pressure switch on the pump is set to shut
off at 55 psi. If the switch or by-pass
are adjusted too much, the by-pass and
switch shut-off can overlap and THE
PUMP WILL NOT SHUT OFF....WARNING: If full by-pass is reached before the shut-off setting, the pump will not shut off. Full by-pass pressure setting should be at least 10 psi higher than pump shut off pressure."

Shurflo operation manual and adjustments:
https://www.pentair.com/en-us/products/residential/water-supply-disposal/recreational-vehicle/shurflo-revolution-4008-series-by-pass-pump.html?queryID=db4b20705223bbb3e90973034b84ba63&objectID=https://www.pentair.com/en-us/products/residential/water-supply-disposal/recreational-vehicle/shurflo-revolution-4008-series-by-pass-pump.html&indexName=prod_pentair_products

[midnightsadie]

from what you say, theres some thing leaking. thats what the pump is telling you.could be a lot of things,

[MDKMDK]

Is there a water filter located under your sink somewhere. In my rig its's under the galley sink. Check that for leaks/cracks/that it's securely tightened. If it wasn't winterized recently, it could have frozen and cracked. They do get missed sometimes.
Is the water pump filter/screen inside the little plastic igloo securely tightened? No idea where your pump is located or how difficult it is to reach, but check it if you can. Also, I've sometimes had the pex water hose connectors loosen at the inlet/outlet fittings at the water pump. Check for tightness. I'll assume you know all of this, because you've replaced it once already.
Have you checked the intake hose valve if your fresh water system came equipped with a syphon tube and valve, to let you put RV AF in the tank when winterizing? Just another useless sinlge point of failure, if you ask me.
Lastly, check the pex fittings on the input/output hosess at the water heater. I had a brand new class A a few years ago, that came from the factory with some of the hoses barely hanging on to their water heater fittings.
Check those items, if you haven't already.
Sorry, best guesses, as it's hard to troubleshoot over the net.