Fixing a Grundfos CU301

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SSmith

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I think that my Grundfos CU301 2-gallon tank is waterlogged, as the pump cuts in and out when running water.

It would be greatly appreciated if someone could post the steps to de-waterlog my tank.


Thanks
 

Craigpump

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You throw those little buffer tanks away.

Sounds like there is a malfunction with the control unit or the transducer.
 

SSmith

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You throw those little buffer tanks away.

Sounds like there is a malfunction with the control unit or the transducer.

This is a new control unit.....I would like to know if the tank is waterlogged, I want to try that first, so how can I do this.....
 

Craigpump

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Take a small screw driver and push down on the core in the snifter valve on the tank. If water comes out, the bladder or diaphram is bad.

Those tanks need to have a precharge of 70% of shut off pressure. 70 psi shut off would be 49psi precharge.
 

Valveman

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Even if the bladder in the tank is busted and the tank is waterlogged, that controller should hold a steady pressure while you are using water. However, when those CU301 controllers malfunction they revert to cycling on and off like a pressure switch with 15 PSI between on and off. If the bladder in the tank was not busted, it will be after the CU301 bounces the pump on and off like that for a short while.

It doesn’t matter that the CU301 is new. When they lose communication with the electronics in the motor, they begin to cycle the pump on and off as a default. Because they use the same wire that powers the pump for the communication signal as well, this lose of communication is a common occurrence.
 

SSmith

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Take a small screw driver and push down on the core in the snifter valve on the tank. If water comes out, the bladder or diaphram is bad.

Those tanks need to have a precharge of 70% of shut off pressure. 70 psi shut off would be 49psi precharge.

I pressed in on the snifter valve and no water came out, so that must rule out the bladder being bad......

So what do I need to do now to get the tank up to 49psi precharge, we live out in the boonies so I am going to have to do this myself....

Thanks
 

Reach4

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To set the precharge on a pressure tank, turn off the pump. Release the water pressure by opening a valve. Add with a tire pump, or remove air from the Schrader valve, and measure the pressure with a tire gauge. I guess it would be good to have an accurate tire gauge.

Do not measure or change the air pressure when you have water pressure. When done, put the cap on the Schrader valve, and turn on the pump.

I have not used your kind of pump, but setting the precharge method is going to be the same.
 

Mliu

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I pressed in on the snifter valve and no water came out, so that must rule out the bladder being bad......
Did you just depress the valve very quickly or did you let a good blast of air out? Even if the bladder is bad, there could still be an air bubble trapped in the tank, so if you just let a squirt of air out, you may not know the real condition of the bladder. Recharging the tank is simple so you might as well do a solid test by letting out a lot of air. It should be completely dry with no water spray or spurting.
 

Valveman

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I pressed in on the snifter valve and no water came out, so that must rule out the bladder being bad......


When those CU301 controllers malfunction they revert to cycling on and off like a pressure switch with 15 PSI between on and off.
It doesn’t matter that the CU301 is new. When they lose communication with the electronics in the motor, they begin to cycle the pump on and off as a default. Because they use the same wire that powers the pump for the communication signal as well, this lose of communication is a common occurrence.

It sounds like your CU301 has lost communication with the electronics in the motor. I think the latest version (generation 7) will cycle like that 1000 times before it tells you it has lost commincation.
 

DJFluck77

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I have a Grundfos Cu 301 and the voltage alarm keeps blinking and the pump won't run. I tried turning off the power at the fuse box (to reset it)and it still doesn't work. When the water softener came on it worked. Three hours later the voltage alarm came on again and it stopped working. Is it time to get an new control unit? It is a ten year old system and was told it would last over 20.
 

Valveman

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A lot of people will replace those controllers 3-5 times in 20 years. I recommend doing away with the CU301 box, adding a regular 40/60 pressure switch, and using a Cycle Stop Valve to control the pump and deliver constant pressure. 20 years would not be uncommon that way.

This kit has everything you will need.
https://cyclestopvalves.com/pages/pk1a-pside-kick
https://cyclestopvalves.com/pages/reviews

But you could go buy a regular 40/60 pressure switch, do away with the CU301 box, and have water in a few minutes. Just let it cycle a few days until you get the CSV installed and you will see the benefits of the CSV instantly.

 
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