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Fixing Hot Tub FLO Errors

Flow errors (commonly displayed as either FLO, FL, FLOW or LF) are the most common hot tub error codes that we come across. In this article, we will show you how to troubleshoot and fix flow errors in your hot tub, regardless of the make and model. But first, what causes flow errors in the first place?

What Causes Hot Tub Flow Errors?

All hot tubs have sensors which are used to monitor the water flow through the hot tub’s heater. Flow errors occur when these sensors don’t detect enough water flowing through the heater.

The reason why sensors specifically measure the water flow through the heater is that without proper water flow, the heater could heat the water within it too much; potentially melting the plumbing or causing damage to the surrounding equipment.

Although they’re only caused by one thing – the flow sensor(s) reading low water flow – there are actually several potential causes of flow errors in a hot tub. So how do you diagnose and fix a flow error? Follow this 5 step process.

Step 1 – Check The Water Level

The first step when troubleshooting hot tub flow errors is to check the water level in the hot tub. If the water is less than halfway up the opening to the skimmer/filter area, there simply may not be enough water flowing through the filtration system. Refill your hot tub to the appropriate level, shut the power down for at least 30 seconds to reset the error code, then turn the hot tub back on. If the flow error returns, go to step 2.

STEP 2 – Check Your Filter

The most common cause of hot tub flow errors is simply dirty filters. As water passes through the hot tub filters, the filters catch and hold onto dirt and debris. As they become more and more clogged with debris, they allow less and less water to pass through them. If they get too dirty they can eventually restrict the water flow enough to cause a flow error.

To fix a flow error caused by dirty filters simply turn off the hot tub, remove the filters, then turn the hot tub back on. If the flow error goes away when the filters are out, give them a deep clean and put them back in. If the flow error comes back with the filters back in the water – or if the filters are over 1 year old – replace your filters.

If removing your filters doesn’t fix the flow error, go to step 3.

STEP 3 – Check The Sensors

There are 2 main types of flow sensors in hot tubs:

  • Pressure switch. These sensors test the actual water flow within the plumbing. As water moves it pushes two tiny metal plates together, completing an electrical circuit that tells the spa pack that there is enough water flow.
  • Temperature sensors. This type of flow sensor measures water temperature in two different parts of the hot tub. If temperatures in one sensor exceed a certain threshold, the spa pack will assume there is no water flow, shut the whole system down and display a flow error.

If your hot tub has temperature sensors, go to step 4. If your hot tub has a pressure switch style sensor you can quickly test to see if it is working by:

  • Shutting the hot tub down.
  • Unplugging the sensor from the spa pack.
  • Running a wire between the two contacts on the circuit board that the pressure switch plugged into.
  • Turning the hot tub back on.

This completes the pressure switch circuit in the spa pack that indicates good water flow. If the FLO error is still there, go to step 5.

If the FLO error is now gone, your issue is with the pressure switch.

STEP 4 – Replace The Sensor

If you’ve determined that your pressure switch is faulty, or if your hot tub uses temperature sensors, the next thing to do is to replace your sensors. When replacing temperature sensors, we recommend replacing both as there is no way to tell if one or both are broken.

Note: Hot tubs with pressure switches still have at least one temperature sensor. These temperature sensors have nothing to do with the sensing flow however so they will not need to be replaced.

STEP 5 – Replace The Spa Pack / Circulation Pump

At this point we’ve exhausted all of the easy options. The cause of the FLO error can now be narrowed down to either a faulty spa pack, or a worn out circulation pump (if your hot tub has a circulation pump). Replacing one or both of them will fix your flow error.

Wrapping Up

In most cases, troubleshooting and even fixing a flow error in a hot tub is something that most hot tub owners can handle. The most important thing to remember when fixing a flow error (or any hot tub error code) is to turn off power to the hot tub for at least 30 seconds before turning it back on. This allows the hot tub to fully power down and reset. If you don’t turn the power of the hot tub off for 30 seconds or more the flow error may remain on the screen, even if you’ve solved the issue.


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