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Hot Tub Pressure Switch Repair Replace Troubleshooting

pressure switch mounted to heaterPressure switches are safety devices in a hot tub to avoid a heater dry fire or overheat condition.

The purpose is to monitor water pressure inside the heater tube and assure it is full of water and circulating properly.  

Normal operating mode for a good pressure switch that is correctly adjusted is that the switch is CLOSED when the water is flowing through the heater and OPEN when the pump/heater stops.

The Balboa system looks for the pump to be running when the pressure switch is CLOSED.  That is when the system can heat.

Newer style Balboa M7 systems have 2 sensors built into the heater tube that monitor temperature and high limit functions and eliminate the need for a pressure switch on those systems.

How the pressure switch works is that it changes between open and closed depending on water pressure.  Sometimes these are called flow switches even though technically, a flow switch operates a bit differently but on the same principle.

The pressure switch is usually mounted on the rear of the flow through heater tube or manifold. Sometimes it is also mounted next to the heater in it's own fitting. 

See all of our pressure switches - we carry most major brands including Balboa, Gecko, Tecmark and Universal pressure switches.

Horse Sense
Warning: Working on your own appliances, cars, covered wagons and hot tubs as well as anything else electrical or mechanical carries with it severe risk of injury or property damage. These tips and suggested procedures are free and for informational purposes only. Proceed at your own risk. It is best to use the services of an electrician or tech. Hot Tub Outpost is not liable for any damage or injury that may result.

adjusting wheel balboaPressure switch adjustment

thumb wheel blackA little thumbwheel is located at the bottom of the switch to manually adjust the sensitivity of the switch. (Some switches have an adjustment screw instead of the thumbwheel).

Sometimes adjusting/recalibrating the pressure switch is enough to get the spa working again.

See Pressure Switch Calibration below for further details.

fl message error

pressure switch adjustError Messages

The topside control error messages on Balboa, Gecko and other control systems such as FLO, FL, FLC or other error that shuts the spa heater and pump off alerts the spa owner to potential trouble with the pressure switch.

FLO-Flashing- Alternates with Temperature Display

On some Balboa systems, the FLO error message alternating with current temperature readout means the pressure switch is open. If the switch is open, the spa will not heat as it is not sensing proper water pressure in the heater tube.  First try to power down and restart the spa.  Maybe the problem will magically disappear! (Sometimes that works) - but otherwise, read on.

closed service valveIf the FLO error occurs, check that water level is at the recommended level (filter/skimmer should not be sucking in air) and that the cartridge filter is clean.  (Replace filter cartridges every year as per most manufacturer's recommendations). 

Also be sure any service valves are completely open/up position and ball valves are completely open to avoid any restrictions in water flow. Suction fittings inside the footwell of the spa should not be blocked.  Is the pump primed and properly working? Be sure there are no air pockets such as can happen when refilling the spa with fresh water.  Make sure that pesky squirrel didn't get in and start gnawin' on your wires neither.

If all the systems look good, then try to recalibrated/adjust the pressure switch using the adjustment wheel at the bottom of the switch. This little black, jagged thumbwheel helps to fine tune the pressure switch sensitivity and is best done with help from an ohmmeter.

FLO-Constant Nothing Works

flow error message panelIf the FLO is solid on the display, then the pressure switch may be stuck in the closed position. 

First check for possible causes above including closed or partially closed service valves, dirty filter, proper water level, pump primed and no air in system, and wire condition.

Has the circuit board been replaced lately? Did the wires go back on the correct terminals of the circuit board?

The pressure switch may need to be recalibrated.  If it cannot be recalibrated, it needs to be replaced.

Just a side note - whenever taking apart spa components, best to snap a picture of how the wires, screws etc. went to refer to in case things get crazy - also best to label all wires before they are removed.

LF - Low Flow

This LF message can be found on newer Balboa control panels that use the M7 system instead of having an external pressure switch. In that case, follow the basic review of checking for low water level, blocked suction fittings, a dirty filter, too many closed jets, a closed service valve or a problem with the main pump that sends water through the heater.  See our page on M7 sensor troubleshooting.

Pressure Switch Testing

flow switch connectorGenerally, if the pressure switch cannot be adjusted, it may need to be replaced - unless the problem is with the circuit board.

The spa tech will start by using an ohmmeter (with the entire spa powered off) and will remove the 1 of the pressure switch wires.  Then measure across the 2 terminals on the pressure switch.  It should be in the open state so there would be no resistance showing up on the meter.  If the switch shows a reading, it needs to be adjusted until the reading goes away (with one wire removed from switch).

Another test performed by skilled technicians is when the spa pump is running at low speed  (still with one wire removed) the ohmmeter should read 0 ohms (no resistance). If the reading is jumping around, then turn the adjustment thumbwheel in the counter-clockwise direction until a steady 0 ohms appears on the meter. Then they will adjust another 1/2 turn or more in the same direction for a little margin.  Note that there is high voltage in the system box, but the pressure switch wires should only have a maximum of about 5 volts on them.

Once adjusted, restart the spa. The electronics will try to sense the open pressure switch (because no water is moving at that point). If it is open, then the pump should start up once the startup routine is complete. If the switch is closed though, an error may pop up on the display again.  Other systems that don't have error messages will just not heat.  Note that Gecko spa packs may show flashing dots near the bottom of the readout/display.

causes of flo

pressure switch troubleshootTest the Sensor Set - For Spa Techs with a spare sensor set

Check sensor wires for cracks or damage that may indicate the presence of a critter.

Inspect the connections of both sensors on the circuit board. The plugs must be clean.

Unplug the sensor set (at the temp/high-limit jumper) and plug in the test sensor set. Hang the test sensors over the
spa side and into the water. Keep in mind there is no high-limit sensor protecting the heater during this test.

If the problem is solved, replace the sensor set. If the problem is not solved, do not replace the sensor set.

Plug in the original sensor set to verify that there is not a connection problem.

If the problem continues after following the above steps, then the circuit board may need replacement.

The Display Continuously Shows FLO or similar error message or the Status/Heat LED is Flashing Briefly On Once every Second.

If this happens, the software is detecting pressure at the pressure switch without the pump running.

Make sure the slice or ball valves are completely open.

To test, disconnect the wire from the pressure switch.

If the spa operates normally, turn OFF the spa system, recalibrate the pressure switch if possible (see below).

If the pressure switch cannot be recalibrated, replace the pressure switch. Clean the area where the pressure switch is located with a metal brush. Use plumber’s sealant (or teflon tape) when installing a new pressure switch.

If the problem continues, then replace the circuit board.

Pressure Switch Calibration - Primer for Spa Techs

balboa ljs jumperThe LJS Logic Jumper Stick by Balboa makes adjusting pressure switches a breeze, so every service truck should have one.

When the display continually shows a FLO error message (solid display) this usually means that the pressure switch needs adjustment or has malfunctioned. When servicing a spa with a solid FLO message:

Disconnect the pressure switch wire at the circuit board. The FLO message will disappear within a few seconds. Now, the pressure switch can be calibrated.

Set the multimeter/ voltmeter to read resistance/ohms.

Attach the pressure switch wire and the 2 volt-ohm meter probes to the Balboa LJS troubleshooting stick (jumper stick). You should see continuity (0 ohm reading).

Rotate the thumbwheel on the pressure switch in the clockwise direction until no continuity is shown on the ohmmeter.

Turn on the high-speed pump (main heater pump) and let it run for at least ten seconds. Continuity should appear on the ohmmeter (0 ohms resistance).

Turn off all pumps, and within four seconds, continuity should no longer exist.

If after four seconds, you still see continuity on the ohmmeter, try to re-calibrate the pressure switch.

If it cannot be calibrated, replace the pressure switch.

Why Pressure Switches Fail

set ohms meterThat 1/8" tiny hole can become blocked by all sorts of things including calcium carbonate deposits. The main reason for pressure switch failure is poor water chemistry. Avoid this issue by always maintaining pH and proper water chemistry.

If the display shows a blinking/flashing FLO message, there may be a flow restriction like a dirty, clogged filter. Or it could just be a faulty pressure switch.

If there is a flashing FLO message on the panel, then set ohmmeter to read resistance/ohms and disconnect the pressure switch wire from the circuit board (label wire-take picture of location on board), and turn on the low-speed pump.

Connect the pressure switch wire and ohmmeter probes to the Balboa LJS Logic Jumper Stick.  Now the pressure switch
can be calibrated.

Adjust the pressure switch by rotating the little black adjustment wheel in the counter-clockwise direction until continuity (0 ohms) appears on the meter.

Switch from low speed to high speed on the pump if available and run for about 10seconds, then turn off all pumps.

After four seconds, check the ohmmeter and verify that there is no continuity (infinite ohms - open circuit) showing.

f there is continuity, adjust the black adjustment wheel clockwise until there is no continuity. Retest with the low speed pump on  as

If the pressure switch cannot be adjusted, it will need to be replaced.

replace pressure switch holePressure Switch Summary

Spa Pressure Switch

A pressure switch is the safety device that turns off the heater in case low pressure, no water flow or decreased water flow is detected at the heater. 

The purpose of the pressure switch is to monitor the heater and plumbing for proper water pressure and to shut off the heater in case proper water pressure is not maintained.

The correct status of the pressure switch is OPEN when a flow problem is detected and CLOSED during heating and normal operation.

Hot Tub pressure switches can be adjusted for sensitivity by a thumbwheel on the pressure switch. These switches are factory/pre-calibrated. Proper field calibration involves powering the spa down and measuring continuity with an ohm meter as the adjustment thumbwheel is turned to set the sensitivity to water pressure properly.

The spa pressure switch turns on when water pressure is detected which closes the circuit and allows the heater and spa to operate normally.

See all of our replacement pressure switches.


ljs stick Balboa