Flow errors (commonly displayed as either FLO, FL, FLOW or LF on your control pad) are the most common hot tub error codes that we come across here at The Spa Shoppe. In this article, we will show you how to troubleshoot and fix hot tub flow errors, regardless of your make and model. Before we get to that, however, it is important to know what causes flow errors in the first place.

What Causes Hot Tub Flow Errors?

All hot tubs have sensors which are used to monitor 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 measure the water flow through the heater specifically is that without enough water flowing through it, 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 hot tub’s control system, 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 the filters get too dirty they will eventually restrict the water flow enough to cause a flow error.

To test to see if a flow error is being 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 then the filters are the issue. Try giving them a deep clean with a garden hose (or better yet with a filter cleaning attachment like the Filter Flosser) and put them back in. If the flow error comes back with the filters after you’ve cleaned them – or if the filters are over 1 year old – you will need to 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 flow sensors designs in hot tubs:

  • Pressure switches. 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 is 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. Replacing it should solve your issue.

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 will 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

If your hot tub is still displaying a flow error after replacing the sensors, the cause of the FLO error can 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. It should be noted that these are expensive components and you should consult with a hot tub repair professional before attempting to replace one on your own.

Did You Just Refill Your Hot Tub?

Another very common reason for hot tub flow errors is when air gets trapped in the pumps after a drain and refill. If you get a flow error after draining and refilling your hot tub, this is almost certainly the reason. To fix your flow error first turn off the power to the hot tub, then slowly loosen the fittings on either side of the pump until you hear air escaping and water leaks out. When you stop hearing the air escaping tighten the fittings again and turn the hot tub back on.

To prevent flow errors like this in the future simply fill your hot tub from the skimmer area first so that the pumps fill with water before the rest of the hot tub.

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 without professional help. Following this 5 step process will allow you to properly diagnose and (in most cases) fix your flow error.

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.

The Spa Shoppe

(905) 666-5333

1545 Dundas St E
Whitby, ON L1N 2K6



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