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Ask Dave: Why does my water pump cycle every few seconds?

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. Today he discusses a water pump which cycles every few seconds, with no apparent cause.

Dear Dave,
Thanks for joining RV Travel – I’ve really enjoyed your columns. My question: We have a 2018 Thor Freedom Elite on a Ford E-350 chassis. It has a Shurflo 4008-101-A65 water pump rated at 3 gpm and 55 psi. The pump pumps fine with plenty of flow. The problem: When there is no demand for water, about every 10 – 15 seconds, the pump “burps” or cycles for about one second. I have found no leaks or evidence thereof and no faucets or the toilet are leaking.

While there is no problem with leaks or water delivery, it is kind of annoying. Any suggestions? Thanks. —Don

Dear Don,
Thank you for the welcome. Your pump is an on-demand type pump and when the switch is on, it senses pressure in the outgoing line and stays put. When you open a faucet, the pressure drops in that line and turns the pump on.

The first thing I would do is remove the pump and bench test it to find out if the pump is not holding pressure. There is a check valve and diaphragm that can get clogged with sediment, rupture slightly, or it could have frozen in the winter.

Make sure you test the screen, as well, when you bench test it. If it still cycles, purchase a new diaphragm kit and replace it. These are very easy to rebuild. Some models have a pressure switch adjustment screw that can be adjusted with an allen wrench, so check for that and make sure all screws are tight.

If it does not cycle on the bench test, then there is a leak somewhere in the plumbing system. We had this exact situation with a 2003 Winnebago Brave and it was quite a search for the culprit. We started with the shower as it seemed to have a slight drip after turning off the shower. This could be a source as you would typically not look in the shower. When the switch was turned off, naturally it did not cycle, so the water could have dried up before looking in there. We put all new seats and parts in the faucets and that did not fix the problem.

Another area to look at is the toilet as water could trickle past the flush ball and ball seal if the water valve or pedal is leaking.

Ours turned out to be the city water to fresh water fill valve. When connected to city water, this model can fill the fresh water tank without removing the hose and using the gravity fill. Simply turn the switch lever to tank fill and it will fill it when the water supply is turned on. The issue we had was it would not seal tight when the switch was in the city water position, so I believe air would leak in and release pressure. We replaced the switch and it worked as designed. We got lucky, as the suggestion came from Owner Relations at Winnebago.

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chris
1 month ago

Likely you have a leak.

CLeeNick
1 month ago

When our pump started cycling on the second or third trip out on our then brand new Passport travel trailer, it turned out to be plastic chips/shavings caught in the pump’s diaphragm that were sucked into the pump from the fresh water tank. RV manufacturers apparently don’t do a good job cleaning the tanks out after they drill all the holes for the fittings (and they don’t always install a filter screen), so the plastic chips/shavings remain and get sucked into the pump, particularly when the fresh water tank runs low. I took the pump apart and used a toothpick to carefully poke out the shavings, and the pump worked fine again after re-assembly. I installed a filter screen (Cheap!..RV makers should be required by the pump manufacturers to install them, because they apparently get a lot of warranty claims for bad pumps because of the chips left by the RV maker), and have never had any trouble since.

DW/ND
1 month ago

First – apply the K.I.S.S. principle! Adjust the pump if able. Check the outside shower, the water heater relief valve and all the other outlets. Second – If all that fails remove it and bench check. Third – take it apart! (Take pictures!)

Clint
1 month ago

Had the same problem with a Shurflow pump. Turned out the pressure was set too high which caused the pump to cycle to try and keep up the pressure. There is a pressure adjustment valve on the pump. A half turn with an Allen wrench fixed the problem and there was still plenty of water flow.

Maurice Valois
1 month ago

I had the same issue on my Montana High Country. I turned the lever to fill my fresh water tank from the city water hose (the first time I’ve had that feature), and when it was full I turned the water off and removed the hose. Pump kept burping every minute or so. I went out and turned the lever back to the city water side, problem solved.

Kenneth Fuller
1 month ago

My pump will burp like that only because I turn off the hot water heater when I’m finished using it. As the hot water cools down, it looses the expansion it caused while heating and the pump will burp periodically until the pressure is equalized.

wanderer
1 month ago
Reply to  Kenneth Fuller

Ah! That might be what’s going on with mine, I do that. There will be one or two brief pump runs late in the evening, not enough to start a hunt for leaks, but enough to make one worry a bit. Thanks for the idea, I’ll run some tests on that.

Leonard Rempel
1 month ago

The exact same thing happened to me when I picked up my brand new Montana last summer. It was a simple as we had the selector valve to “fill”, when we should have had “city water” selected. Yup,it was that simple.

Tom
1 month ago

A leaking ball valve will not have anything to do with the water pump operation. If the ball valve is leaking, the bowl will be “dry”, as the water will drain out and end up in the black tank.

If the water supply valve is leaking, the bowl will “fill”, possibly to overflow, as there is no place for the water to go, except into the bowl.

The two systems are in no way related.

Michael
1 month ago
Reply to  Tom

I thought the same thing when I read it.