Weird water problem

[Steph and Dud B]

We just arrived at a dry camping site. Full water tank, plumbing, and water heater tank from the previous trip. Water heater running on gas. Weird #1: For a surprisingly long time cold water was working without the pump coming on. But then: turned on the kitchen cold water, no pressure. Have seen this before. For some reason we get air bound. Went outside and opened the cold water outside shower. No pressure, just a dribble.  The pump kicks in, but sounds like it's pumping air. Here's the second really weird part: the dribble of water I'm getting from the cold water shower is hot! Yes, the hot water valve is off. I go inside. Turn on the cold kitchen faucet. Now the pump sounds normal and water pressure starts to build. Open the hot faucet, get lots of pressurized air from the hot lines, then it sputters, then finally everything is normal. 

How on earth was I getting a dribble of HOT water from the COLD water shower tap?? Was the water heater pressurizing the system, causing cold water to flow for a while without the pump. Did it then backfeed into the cold water lines?? What is going on here?

[jd1923]

5 hours ago, Steph and Dud B said:

How on earth was I getting a dribble of HOT water from the COLD water shower tap?

A small amount of hot water can pass through the kitchen faucet valve. Those lever-operated combination valves will do that, even a "dribble" when new, more when the internal O-ring seal wears with some age.

The real question is why the cold ran so long without the pump kicking in. The cut-in pressure did not work correctly on your water pump allowing the cold side to drain completely. Given this has happened before, you likely need a new water pump.

It kicked in later when at zero pressure and likely water leaking in from the pressurized hot side backfilled the cold allowing the pump to prime. Just my hypothesis. Could also be you run more often on City Water and the pump pressure switch got stuck from lack of use.

Either way, I would replace your water pump, knowing this is likely to reoccur. I also suggest replacing with an upgraded model over the OEM pump. You can add 5 PSI with no ill effect on the plumbing and go +1 GPM for much improved performance. Water pumps are relatively cheap and an easy swap.

[Cameron]

Agreed. I was having some strange behavior with my original water pump. My trailer's a 2021, so I couldn't believe that the pump was going bad. Well, I changed the pump and suddenly had no problems. I kept the old pump, don't know why, but at least the water system is working properly!

[GraniteStaters]

There is a kit available to rebuild the diaphragm pumps for Shur-Flo.  It a very straightforward rebuild and worth it if the pump motor is working.  The part is very compact and is good to have in the vehicle if you don’t travel with a spare.  

[jd1923]

13 hours ago, GraniteStaters said:

There is a kit available to rebuild the diaphragm pumps for Shur-Flo.

I'm not well versed on RV water pump internals. Thinking that if the pump needs rebuilding though it would run on, for not building up pressure and/or produce less GPM. There is a set pressure for these pumps to kick-in. If pressure is regulated by the diaphragm, then this kit could do it. But I'm thinking there is an independent pressure sensor that a pump rebuild would not correct.

@Steph and Dud B's pump motor twice did not activate when it dropped well below pressure. I replaced my working OEM just to improve performance. My hull is older and hopefully a 2022 hull would have a better OEM pump than this. 

[Geronimo John]

Before doing too much, suggest verifying all the water valves in the curb side rear bunk area are fully turned in the proper direction.  If one is partially shut WEIRD things happen.

GJ

[Jason Foster]

I had a pump that turn on and off every hour or so.  I also thought it was a bad pump.  Turned out the toilet flush valve was leaking.

[jd1923]

13 hours ago, Jason Foster said:

I had a pump that turn on and off every hour or so.  I also thought it was a bad pump.  Turned out the toilet flush valve was leaking.

This is the basic symptom of a plumbing leak. The leak causes a loss of pressure in the lines. Pressure drops below the set pressure and the pump kicks in to recover, just like when water is being used.

The "weird water problem" cited above was the opposite issue, where the pump would not turn on with loss of line pressure.