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Old 02-01-2022, 10:18 AM   #1
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Water pump runs continuously

If my holding tank is full, all is well. Once the level of the water in the tank drops below the pump, my pump will start to occasionally run continuously, without actually moving water, until I turn on a faucet, then it will eventually prime and start moving water.


As the water level drops, the delay gets worse. Once I'm down to about 15% full, it won't prime and will just run continuously. If I do get it primed, it will pump the tank completely empty if I let it. It's only when I turn off demand that the pump runs without priming. Once I do get it primed and pressure comes up, if I turn off the water, then turn it back on right away, it works as expected. The longer I leave the faucet off, the longer the delay before it will prime and build pressure.


I've replaced with a new pump but it does the same thing.


I called Shurflo and he said he has no explanation and no suggestions to try to fix this.


I have checked and the inlet screen is clean, and it doesn't seem to be sucking air anywhere, and the pump isn't leaking.


I ended up removing the air inlet hose at the top of the tank to verify it isn’t clogged.

I removed the outlet at the bottom of the tank to verify it’s not clogged, then replaced it with a new fitting, a new section of pex to a new ballcock, then reinstalled the reinforced vinyl hose from there to the pump strainer. After filling the tank I noticed I didn’t have the band clamps tight enough, so I tightened all of them as tight as I could get and the leaking seems to have stopped.


However, the problem persists. As the tank empties, the time to prime goes up and nothing really has changed. I’d previously run every faucet to clear any air out of the lines and that didn’t help.

The faucet will occasionally spit some air when running, so it must be getting air in the line somewhere, but I can’t find a leak, and have no idea where/how to look to find it.

I plan to eventually replace all the plumbing with new pex to eliminate the hundreds of elbows and tees they installed and just run continuous pex with bends and no fittings, between the terminations, but until that happens, I really need to get the system working properly.

I appreciate any help or guidance you can offer me.
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Old 02-01-2022, 10:24 AM   #2
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New pump....same issue

But is the inlet strainer same old one?

O-ring leak, cracked strainer----faucet spits air----leak on suction side of pump
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Old 02-01-2022, 10:30 AM   #3
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The only place for it to bring in air is between the water tank and the pump inlet, somewhere in that run there must be a slight 'leak'. That's the low pressure side of the pump so a leak in that run may not show any water, and only becomes a 'leak' when it lets in air as the pump is trying to pump water. (A leak after the outlet side of the pump would let water out of the lines, but it wouldn't bring air in)
First thing then is to triple check all of those fittings between the tank and the pump. If possible remove the strainer just to reduce the number of connections.
Next thing I'd try is to lower the pump so that it doesn't have to pump uphill to get water out of the tank. Try just laying the pump on the floor there to see if that changes anything (I realize that will mean you have to do something different on the outlet side of the pump to get it connected with the water lines)

Edit: oh sure, O-B jumps in there with a short email while I'm writing more details. But hey, at least we two agree on where the issue is.
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Old 02-02-2022, 06:50 AM   #4
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Thank you both for the feedback. I took the strainer apart to check the o-ring and screen and a part of it fell out into my hand. The bit that fell out was the bottom of the female thread, which seems to be completely inside the strainer, so that shouldn't be the issue, but the fact it's broken tells me it needs replaced, and might have other stress cracks I'm not seeing. I ordered a new strainer and will hopefully replace it tomorrow. I will remove the other fittings and probably that section of vinyl hose and replace with new hose and band clamps and that will hopefully make it all good again.


The lack of visible water leaking was probably what threw me off, but yeah, it makes sense that that must be where the leak is.


I very much appreciate the help, thank you!
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Old 02-02-2022, 08:06 AM   #5
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It took me awhile studying your pictures before I understood what I was seeing. It appears to me the tank is tall and narrow. I can see water in the tank about 2/3 full. All RVs I've seen had the water pump situated at the so it's input was the same level as the tank outlet.

I think that your problem is compounded by the mounting position. The inlet to the pump is considerably above the outlet from the tank. When the tank is full gravity causes pressure into the pump inlet. As the tank level drops the pressure caused by gravity decreases until the point where the water level in the tank is the same height as the pump inlet. Then as the water level continues dropping the pressure at the pump inlet goes negative and the pump is required to lift the water. Water is heavy and lifting is difficult. The lower the level of water in the tank the higher the pump must lift the water. A pump without prime must create a large enough vacuum to overcome the weight of the water. It takes a very good pump working hard to do that. When the pump is not pumping the slightest pin hole will leak enough air to break the suction at the pump inlet allowing the pump to lose prime.

I think if you can find a way to mount the pump so the pump inlet is level to or very close to the level of the water outlet on the bottom of the tank your problem will go away. Try lowering the pump as close to the floor as possible. If you do that gravity will feed water into the pump inlet all the way to the bottom of the tank. This change will make it much easier for the pump to prime because the pump will not be lifting water. It will also reduce the negative pressure at the pump inlet thereby reducing the chance of losing prime.

The best mounting position for the pump would be on the floor if there is enough room. Mount the pump so the pump inlet is pointed directly at the tank outlet.
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Old 02-02-2022, 08:22 AM   #6
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I totally agree on just dropping the pump to the floor level. Problem will likely disappear.

Or try a piece of hose you can put some loops into. Just a loop or two. When the pump shuts off the loops will hold some water to allow the pump to start sucking and it will not have to lift water as high. If this makes sense.

But putting in on or close to the floor should help.

There are kits sold that help reduce the rattling noise when these pumps run and they are simple flexible hoses that have you put the loops in them. It is not for priming as such but if you put the pump on the floor or very near you may find this helps as well.
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Old 02-05-2022, 08:47 AM   #7
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the new strainer arrived and easily installed. I didn't move the pump, I just cut off the end of the hose that connected to the old strainer, in case it was an issue with the hose and installed that to the new strainer inlet.


It's taken a couple of days to use enough water to get the tank to where the problem would start, and the problem is gone. The holding tank is now virtually empty and the pump still starts immediately and shuts off immediately when the faucet turns off.


the pump is a bit quieter also, which is a nice bonus.


Sadly, this has all led to a different issue. The pump is now cycling when using the shower, which seems to only change the flow of cold water, so it's impossible to maintain a set temperature when showering, which is not great.


I started a new thread about it.
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