One of the more common hot tub service calls I get here at Precision Pool is for a spa that isn’t heating due to a low flow error. A lot of times the customer won’t know the tub is giving them a low flow error, and only that the tub has not been heating and the temperature is down below the desired range. Before we get into what causes a flow error and how to fix it I should probably explain what a low flow actually is.
What is a hot tub flow error?
On either side of your spa’s heater there are two sensors that read the water pressure flowing through the system. You can also have something called a pressure switch located on your heater element which does the same thing.
These sensors are there to protect the heater from running dry, so if the water flow drops below a certain level the sensors will tell the heater to shut down in order to protect itself from burning out.
You see if the flow is not at the desired level there is usually a good amount of air in the lines, when a spa heater or motor is running with air in the lines we call this running the system dry.
When the system runs dry the components heat up and can eventually burn out, permanently damaging the equipment. The flow sensors help prevent this from happening by shutting the heating system down when the flow is less than nominal.
What causes a hot tub flow error?
There are a couple of common causes for flow errors in hot tubs; low water level, dirty filters, clogged circulation pumps, and bad flow sensors. Filters are usually the number one culprit as people don’t take the time to clean the cartridges often enough so the pleats get clogged and restrict the flow.
Water level is also a common factor in flow errors, even with an insulating cover there is a lot of evaporation and that can lead to significant loss of water. If the water gets too low and the spa’s filter well is not completely submerged it can cause air to be drawn into the system giving you a low flow error.
How to troubleshoot a low flow error
So lets say you go out to your hot tub, lift up the cover and you notice the temperature is low and your topside control is flashing some lights at you and reads “lo flo”, what do you do now? The steps laid out below is what I have all my customers do when they call me for a low flow error.
- Step 1.
Check your spa’s water level, if the water level is too low turn off the spa at the GFI, fill the spa, and then turn it back on.
- Step 2.
If water level is not the problem you should remove the filter cartridges from the spa. Wait up to 1 minute to see if the error clears itself,if not reset the tub by turning off the GFI breaker, wait 1 minute, and then turn the breaker back on.
This process will clear the PC board of the error and if the filters were the culprit, your spa should start heating and running normally. At this point you should soak you filters in a cleaning solution and rinse thoroughly before placing them back in the tub.
- Step 3.
Check flow sensors or pressure switch to make sure they are working properly and not causing a false error. These parts are easily and inexpensively replaced.
- Step 4.
If you have a small circulation pump in your spa this could be clogged with debris and causing low flow. If a circulation pump is bad you can usually hear it whining when it is running. This whining sound can be a sign of a clogged impeller or a bad motor.
At this point if you are still having a low flow error I recommend calling your local spa service tech or the dealer you bought your hot tub from.
From here the troubleshooting takes you inside the spas service area and should be looked at by an experienced technician.
An important thing to remember is every time you try one of the troubleshooting steps you should reset the tub’s GFI breaker to clear the error out of the topside control.
Going into detail troubleshooting of flow sensors and pressure switches are two blog posts of their own and I hope to get to that in a future post. For now if you have tried pulling the filters and your water level is fine my advice would be to call an experienced technician to troubleshoot the issue.
If you are a die hard do it yourself’er and want some guidance through the troubleshooting process feel free to send us an email at: [email protected] Please make sure to include your spa make and model in the email.