Pump issue

[DGL]

I have a 2600 gal underground concrete cistern that feeds to a Grundfos MQ3-45 Pump that feeds my 1000 sq foot cabin. We just moved in 5 weeks ago and the system worked great until a week ago when we lost all water. I went down below the cabin and the pump had the alarm light on and I realized the plastic suction connection on the pump had cracked. I ordered replacement parts, replaced the connection and the system worked great for a day until we lost all water again. I get the alarm light on. I reset the pump and manually start it but it continuously runs-instead of shutting off after the need of water is fufilled-until it shuts itself off with an alarm light. Grundfos manual says when the pump continuously runs there's a leak in piping or the non return inlet valve inside the plastic suction connection is blocked. I see no leak anywhere. Checked valve it's fine. I'm at my wits end what's wrong.

 

[Sarg]

Have you checked the pressure tank.
The tank air pressure should be set 2 psi lower than the pump switch "on" is set for ........ if your switch is set for 30/50 then the tank air pressure should be at approx. 28 psi.
Air pressure is checked with the water pressure at zero ..... turn off the pump and open a faucet to drop the water pressure to zero ...... then the tank is checked just like a tire withe the schrader valve on top of the tank . ( this assumes you have a bladder or diaphragm type pressure tank )

 

[Sponsor]

 

[LLigetfa]

Have you checked the pressure tank.

I don't think that pump uses a tank.

 

[Sarg]

I don't think that pump uses a tank.

Looks like you're correct as usual. The literature says it has a (tiny) built in pressure tank. All new system to me.

 

[DGL]

I do also have a pressure tank. Check the pressure on that? Make sure it's under 30?

 

[DGL]

It reads 40. Remove some pressure?

 

[DGL]

And when the system ran fine the pressure was at 40 on the dial.

 

[Reach4]

It reads 40. Remove some pressure?

Did you read air precharge of 40 psi while the water pressure was zero?

What is the cut-in pressure for your pump?

 

[DGL]

Didn't help. Still continuously running.

 

[Reach4]

Didn't help. Still continuously running.

Shut off the valve, after the pump, that leads to the house. See if the pump stops then. If not, replace the pump. A less all-in-one unit might last longer.

A horizontal 1/2 hp 10 gpm pump in a flow inducer sleeve would be quieter. It would need a pressure switch at the pressure tank.
https://terrylove.com/forums/index.php?threads/water-system-questions.82708/

 

[LLigetfa]

Those pumps use a combination of flow and pressure to control the pump and are prone to failure. I would replace it with a standard jet pump or a submersible in the reservoir and add a cycle stop valve.

 

[Valveman]

Low pressure or start of flow can start an MQ but loss of flow is the only thing that stops it. The flow switch in the pump is probably stuck or bad, which is just one of many common problems with those type pumps. Here is a picture I use a lot to show where most MQ's end up in a short period of time.

 

[Valveman]

Get a regular jet pump like a Goulds J10S and use a PK1A kit to control it. The pressure will be much stronger and you won't have to think about your pump system again for 30 years.