Why does our Grundfos water pump keep kicking on?

sounds like a pressure cut off switch issue that senses when the water is turned off.

https://www.google.com/search?q=grundfos+scala+2+doesn%27t+switch+off

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There are several possibilities here. All involve water pressure. The first is that you have a water leak between the pump and where the water is going to.
The second is that the pump is not getting enough water to it so it is sucking air well as water in an attempt to give you water perssure. This could be caused by not having an inline "one way" valve on your supply line just before the pump ($30.00).
The third involves two little screws on the control where your electical connection is. These two screws control the high and low pressure settings of your pump. If your high setting is too high the pump will simply keep running trying to do the impossible, If there is not enough difference between the high and low setting the pump will also keep on. running.
Another possibility is that the pump has had debris (sand, dirt, mud, etc) sucked through it and has damaged either the housing or more likely the impeller that spins the water creating the pressure.Ther is also an internal seal that can be damaged by debris.
The final possibility is that the pressure control unit with the two little screws I mentioned earlier has failed and is deffective.

Most importantly if the pump is running hot please stop using it! You are at risk of fire and possibly the loss of your home and loved ones. Grundfos pumps can be serviced by a professional technician, Parts are readily available and not extremely expensive. I would not recommend doing it youself if it is the pump.as some specialty tools may be involved depending on the problem. You will become frustrated very quickly.
A fast solution is to buy one of the cheap plastic pumps ($169.00) made in China. They are amazing for the price and will run with no problems for years if your water is free of debris. Fixing your Grundfos may run you the same amount and you maybe without a pump for a week or more depending on the technicians work load.
I am not saying "Don't fix your Grundfos" but you don't need to be in a panic about it either.

Check level switch.

Is it newly installed or has it been working for a while till you noticed it?

Pressure is bleeding back through the pump or system to the tank or well or where ever the water is coming from. Should be some sort of one way valve to keep water from going back to the source, mounted somewhere so that once pressure is pumped up, it will hold that pressure in the part of the system that has the pressure switch that controls the pump.

That or you have a leak where you can't see it. (Actually you do, it is just internal and not leaking outside the pipes!)

Grundfos said the problem of on off every few seconds was air in the line. Then

later admitted it was the control unit. After replacing two units in 2 yrs I replaced

it with a standerd pump pressure switch.....Runs fine

The check valve is bad. When the system builds up pressure and shuts off the check valve prevents water from dropping back down the well line. When the check valve goes bad water drops back down the well line and siphons water back out of the well tank causing the switch to kick on and off constantly. The check valve will between on the well line coming from the drop pipe. It may be making a constant rattling noise as pump is running. Replace the check valve and you should be fine. Also check the pressure in bladder tank it should be 2psi below the "cut-in" pressure for the switch.
RJ

It sounds like there is sediment in the pump housing. Take it apart and clean out the area the impeller runs in or failing that change your pump

I have circulation system on my water heater.
First system gave out.
When taken apart, it was clogged with sediment and couldn't be cleaned.
Put sediment filter on line, and second circulation system works fine, and timer works fine too.
I haven't had timer problem, but have investigated timer motors running fast and slow.
My friend who re-winds big pump motors says homeowner timer motors are engineered for 60Hz.
As long as electric power is 60Hz (60 cycle AC), then motor will keep exact time.
Since your household current is 60Hz and other electro-mechanical timers run correctly, then it's likely timer motor has a flaw or has gone bad.
Grundfos water heater re-circulation pump and timer are sealed unit.
Grundfos manuals do not show parts list or repair steps:
http://waterheatertimer.org/Water-heater-recirculation-system.html#Grundfos
It's aggravating when expensive household timers like Malibu power packs and Grundfos pumps are not made to be repaired.

Grundfos is a sealed unit and not a repairable item.
The timer dial should turn.
And pins located around dial control ON-OFF functions as timer dial rotates.


Does the receptacle have power?
If receptacle has power, and Grundfos is not working, then it is broken.
Grundfos manuals for UP series pumps do not show breakdown or parts list of any kind.
http://www.us.grundfos.com/web/download.nsf/Pages

Bigger question:
Why don't you have hot water?
Is water heater functioning?
Water heater is a separate appliance from Grundfos pump.
Grundfos pump circulates hot water from tank into the lines so there is no waiting for hot water ... but hot water heater should still make hot water.
http://waterheatertimer.org/Water-heater-recirculation-system.html

Add a comment about water heater if that is also a problem.
You could have 2 problems, and water heater is main issue.

For do-it-yourself electric water heater repairs:
http://waterheatertimer.org/6DIY.html