DiagnosicLogo  Diagnostics

Spa Repair Diagnostics-Pressure or Flow Switch



Failure Of Pressure Switch or Flow Switch
PressureSwitch  FlowSwitch 


A failure of either the flow or pressure switch usually creates an error code on our topside. Common flow error codes are FL, FLO, PS1, PS2, or the like. If you are getting that error it could be the pressure of flow switch.

Your hot tub has either a pressure switch or flow switch. The purpose of either is simple: tell the board if you have enough water moving to turn the heater on. Its the spas first protection from causing a meltdown or fire because of lack of water flow.

Your control system will likely follow this order: When you first power up and all pumps are off it will check the flow or pressure switch. Because of no water flow the switch on most models should be OPEN. If closed you will get some FLOW error. Often its a solid flow error but see your manual for help. What the unit does is "looks" at the switch before it turns the pump on. If the switch is closed the spa will see that as a fault and either completely not come on or only partially. And give you a pressure/flow switch error.

If the spa passes the first test it will turn on the circ pump or low flow pump and AGAIN look at the pressure/flow switch. Now the switch should be CLOSED. If it is the control will turn on the heater. If the switch is not closed the control will not turn on the heat and give you another FLOW error.

NOTE: If the flow error only comes on AFTER the pump comes on and you can SEE the pump come on and water moving, try removing filter(s) and see if that resolves. If not, see adjusting the flow switch below.


By their name you can tell how pressure and flow switches work. First, the pressure switch works by water pressure. When the pump is OFF, no pressure so the micro switch is most commonly in the OPEN position. When the pump turns on, pressure is created, and the switch closes. The flow switch works a bit different. When the pump is off, the flap with a magnet is bent away from the stem which has a reed switch. In that position the circuit is open. When the pump is turn on, water flow moves the flap flat against the stem and the reed switch closes. Both the pressure and flow switch perform the same function in different ways. Flow switch is commonly used in low pressure heating systems.


What happens over time is the on/off/on/off can cause the switch to fail. If you are getting a flow error on your topside then the board is telling you that it will either completely shut down, partially shut down, or just won't turn on the heat (depending on model).


Testing is easy. With power off you unplug the cord from the switch to the board. You set your voltmeter to OHMS. With spa power OFF place the 2 probes of your voltmeter into the switch cord wires. You should have -0- continuity. Note that touching the cord wires might be a challenge. Manufacturers small socket make touching the 2 wires of the cord hard to reach. An easy help I found it take a wire paper clip, unfold it, and break in half. Wrap each half around each meter probe. Now the probes will reach into the pressure/flow switch socket and give you an accurate test. If you test show-0- contnuity, proceed to next step. If you have any continuity (your meter slows some values) replace pressure switch.

With no continuity turn on power to the spa and check pressure/flow switch cord again. You now should have complete continuity -1-. If the meter bounces and you have a flow switch, replace. If it bounces and you have an adjustable pressure switch, carefully turn the adjustment 1/2 turn counterclockwise. If that doesn't resolve replace the switch.



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