What Causes "Water Pump Short Cycling" - a water pump turning on and off too rapidly
InspectAPedia^®  -    

• How to diagnose & correct short cycling "on-off" of the building water pump
• How to adjust the water pump pressure control switch
• How to add air back to a water pressure tank
• Well pump & water tank diagnosis & repair procedures

A defective water pressure control switch. Switch contacts can burn-up, or the opening into the switch which senses the water pressure in the system can become clogged with sediment or debris. This usually shows up as failure of the pump switch to turn on or off at all, rather than short cycling. But the switch could be damaged or improperly adjusted, causing "short water pump cycling."

Technical note: Clogging of the Water Pump Pressure Control Switch if your water has a high level of silt, debris, or minerals, it's possible that the tubing or piping connecting the pump pressure switch to the pump or water piping, or the pump switch bottom orifice through which the pressure switch senses the water pressure in the system has become clogged. The small diameter of this tubing and still smaller diameter of the pump switch orifice makes clogging easy if your well water is high in sediment or minerals.

A clogged water pump pressure control switch will often fail to turn on the well pump at all, even though the pressure in the system has dropped below the water pump "cut in" pressure. Reader Jeff Crosby reported an example of this pressure switch clog problem:

[When our well pump kept short cycling and I was unable to get the well pump pressure control switch to work properly, ...] I ended up calling the pump service company to come over. There was an extreme amount of mineral buildup inside the pump where the copper tubing initially comes out to travel to the pressure switch. I thought about checking that out but did not know how funny. There has always been an awl sitting on the pump base for the longest time. One of their maintenance guys left it there long ago. Now I know why - ever since that date when they come do their yearly check up they knock out this sediment [using the awl to open the tubing so that the pressure switch can accurately sense the water pressure in the system]. -- Jeff Crosby

On rare occasions we can tap on the well pump control switch and it will begin working again, but not for long, and not reliably. Another water pressure control switch failure is the rupture of a rubber disk or "bladder" inside the switch itself. If you detect or suspect a defective pressure control switch, try replacing it with a new one.

We see a similar problem affecting water pressure gauges on private water systems: debris or mineral deposits can clog the pressure sensing orifice on the water pressure gauge, causing it to fail to respond at all, or to respond inaccurately to changes in water pressure.

When we find a clogged water pump pressure switch or the tubing connected to it, or a clogged water pressure gauge, we replace those items. A well pump pressure gauge that does not respond to pressure changes is potentially unsafe as it could lead to excessive pressurization of the water tank and building piping.

A clogged water filter can block water flow between a pump and water tank or between a water tank and the rest of the building. Try changing the water filter by installing a new cartridge; temporary diagnosis can be made by simply removing a suspect water filter cartridge from its canister entirely. I've also seen a clogged water filter cause water pump short cycling, with a rapid "on-off" pump cycle (which is bad for the pump and pump relay switch.)

Tips for diagnosing water filters as a cause of well pump short cycling:
If your water filter has a bypass valve, try opening that valve to see if the short cycling stops. If there is no bypass valve for your water filter, turn off the pump and valves around the water filter, then remove the water filter cartridge and reassemble the unit. If the short cycling problem stops you probably had a clogged water filter. Replace the water filter cartridge.

• Technical note: the same clay, silt, or other debris that clogs a water filter can clog up the pressure sensing opening in the bottom of a pump pressure control switch, as we discussed just above. So if you are looking for a clogged filter, if changing the water filter does not correct a problem with the water pump cycling operation, also consider a possibly-clogged pump pressure switch.
  
  

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