Pressure Switches

Aug 1, 2021 By The Clozer


The pressure switch is like a light switch and tells your pump (jet or submersible) to run or not to run.  It is most likely located (attached) to your jet pump motor, or in the case of a submersible pump, located at the pressure tank.  It will have an electrical wire running to it which will be controlled by either a plug, switch, breaker(s) or fuse(s). 

The pressure switch basically monitors the pressure in your water system.  When the pressure drops to a pre-set pressure, the contacts located in the pressure switch close, sending power to the pump, which will run until the pressure rises to the pre-set shut-off pressure, at which time the contacts will open.

Most pressure switches operate on a 20 PSI differential between OFF and ON.  In other words, your pump might come on at 20 PSI and shut off when pressure reaches 40 PSI.  These settings can be 20-40, 30-50 or 40-60.  These are the most common settings.

There are many conditions that can cause a pressure switch to malfunction;

  1. Plugged fitting or tube connecting the pressure switch to water system.  A plugged pressure switch can have dirt, rust or corrosion within the switch itself.  Since the pressure switch is operating by sensing the pressure in your water system, it is important that these things are clear.  If partially blocked, there may be a delay in your pump starting or stopping.

Common blockage locations are a) where the fitting connects the tube to the jet pump body b) where fitting connects to the pressure switch or as mentioned, inside the bottom of the pressure switch where the pressure sensing diaphragm is located.


  1. Pressure switch is "Jumping" or clicking on and off when the pump starts.  This means the contacts are opening and closing quickly.  This usually happens because the pump can't discharge water quick enough.

Cause can be that there is a restriction on the discharge side of the pump, leading to the pressure tank or a waterlogged pressure tank.  In these situations, the pressure switch doesn't know how to react and will cause "jumping".  Check to see that the fittings between the pump and pressure tank aren't "closed up" (usually galvanized fittings).  If the pressure tank is a bladder type, it will need to be replaced, as adding air to the tank will not remedy the problem.


  1. Pressure switch has a small lever outside of the pressure switch cover.  This means that the pressure switch has a low water cut-off.  It is a protection for your pump when your water source fails or can't keep up with the pumps demand for water.  A pump running without water will eventually cause pump failure.

Let's say you're at the cottage and the power goes out.  During the outage you have used the water that was stored in the pressure tank, and your system is now at 0 PSI.  The power comes back on, but your water pump doesn't start back up automatically.  Chances are your pressure switch is equipped with a low water cut-off switch.  In this case you will have to operate the lever on the side of the pressure switch and hold it, closing the contacts, until approximately 20-25 PSI is achieved, then release the lever.  The pump should then go back to normal operation until power is discontinued again.  This lever process will also have to be performed on spring start-up.


Jet pump runs and pumps water but will not build enough pressure to shut-off.  One common reason is that the pump has "picked up something".  It may be a twig, small stone or some other foreign debris that has been pulled up the suction line and is now lodged in the pump.  In most cases the debris will get stuck in the injector of the pump, located with-in the pump body.  Since the injector is a main component responsible for building pressure "“ the injector will have to be cleaned.


Some pumps are equipped with an injector that is accessible by unscrewing a plug on the side of the pump body for easy service, eg. Grundfos.


Some pumps have a 1/4" plug directly below where the suction line attaches to the pump, which allows some access to the injector, eg.  Aermotor.  Remove the plug with 0 PSI on the system.  You may be able to free up debris by inserting a small diameter rod to push debris back out of the injector.  A rigid strand of wire or metal meat skewer should work.  The debris may become lodged in the injector again on re-start of the pump since you are just pushing it back and not removing it.  If you're lucky the debris will pass thru the injector and your pump will operate normally.


A majority of pumps that I have dealt with have a "nose" on the pump to which the suction line attaches to.  You may have to remove the two bolts that hold the "nose" to the pump body, to access the injector.  You may want to ensure you have a replacement gasket for the "nose" piece. 


Remember that the debris probably entered the pump thru the foot valve.  Be sure the foot valve has not fallen off the pipe and onto the lake bottom, or that its screen is still attached.  Also be aware that any galvanized fittings in the suction line could be deteriorating and flaking off, causing debris.  These galvanized fittings my be located where the foot valve attached to poly-pipe, a coupling or fitting along the length of the poly-pipe or right at the pump...... Very common!