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What Does the Spa Pressure Switch Do?

The Pressure Switch on your hot tub is a sensor that’s often mounted directly on or next to your heater housing. The purpose of the pressure switch is to shut your heater off in the event low water flow occurs. A built-in safety device, the spa pressure switch restricts electricity from getting to your heater or other components if low pressure is detected.

By monitoring flow rate through the pipes, pumps and heater, the spa pressure switch ensures your spa functions safely. For example, if there is insufficient water flowing through your heater, it could overheat, causing damage to expensive parts.

What to Do When You See “Flow” Message

A "Flow" message on the display of your control panel lets you know that not enough water is flowing through the spa heater. This may be caused by an old or dirty filter or even a faulty pump, which both restrict water flow. To avoid this condition, we recommend cleaning your filters monthly, and replacing them every 24-30 months.

To begin, confirm the spa water level is at the correct height, and not too low. Next, remove the filter(s) and check your control panel. If the "Flow" message error is gone after about 1 minute, clean and reinstall the filter. If the error message returns after the filter has been cleaned, you need a new filter.

The good news is, adjusting the pressure switch can sometimes compensate for this flow reduction and allow the heater to turn back on. However, be sure to cover the basics first. Check your water level, filter(s), and make sure your pump is working correctly before attempting to adjust your pressure switch.

How to Adjust a Pressure Switch

Most pressure switches can be adjusted easily by turning a dial. If a clean filter does not remove the "Flow" error message, let’s see if adjusting the pressure switch helps.

  • Step 1:

    For spas that heat using a large jet pump, the low speed should be operating. For spas using a small circulation pump for heating, confirm there are bubbles shooting in a steady stream near the light. Your spa model may not match the pictures exactly, but the process is the same.

  • Step 2:

    Turn the power to the spa off. Open your spa panel and locate the pressure switch connection on the printed circuit board.

  • Step 3:

    Unplug the pressure switch from the printed circuit board by holding it firmly and pulling straight out; otherwise you may damage the pins on the circuit board. (Your spa's pressure switch connector may be in a different location on the circuit board than pictured here.)

  • Step 4:

    Using sandpaper, carefully clean the two pressure switch pins on the circuit board to improve the connection. (Don't spend more than a few seconds on each pin; it does not have to be perfect, just better.)

  • Step 5:

    Replace the pressure switch connector by plugging it back onto the printed circuit board.

  • Step 6:

    Unplug both connectors on top of the Pressure Switch and sand the prongs on the switch, and wire terminals. Plug the terminals back in, noting that either wire can go on either prong.

  • Step 7a:

    For switches with an adjusting screw, as shown here, use a screw driver or allen wrench to turn the adjusting screw. Turn clockwise 2 full turns.



  • Step 7b:

    For pressure switches with an adjusting wheel, as shown here, lift the stop plate on the back, and turn the wheel clockwise 2 full turns.



  • Step 8:

    Now, slowly turn the adjusting screw or wheel (whichever applies), counter clockwise until you hear the heater relay "click". The heat light should now glowing solid; indicating the heater is on. Make an additional 1/4 turn in the same counter clockwise direction. (Push the stop plate back down if you have one.) We like to put a drop of nail polish on the adjusting wheel or Allen screw to help lock it further in place.

  • Step 9:

    Re-set the temperature to your desired level. If after completing this process, the problem is not resolved, you may need to replace the pressure switch.

Luckily, hot tubs are designed with multiple safety checks in place, like the High Limit Error for excessively hot water and others. Pressure switches are but one safety feature that alert you to a problem, shutting the system down if the water pressure is too low. Knowing how to calibrate a pressure switch can save you time in the event you see a “Flow” message. However, if you need help or would like to talk to one of our technicians, please give us a call. We’re happy to help.