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.

Hot tub low flo error solutions

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.

Dealing with a hot tub air lock? Check out our article: How to release and airlock in your hot tub

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.

  • 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.

  • 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.

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.

About the Author


Jay is the retail sales manager at Precision Pool Construction and has been running the store for the past 9 years. He has been in the pool and spa industry for the last 17 years and is CPO certified by the National Swimming Pool Foundation. In addition to his pool and spa experience, Jay is an accomplished solo singer/songwriter who has been featured on various Boston radio stations and has played in some of the areas best music venues. Check out the tunes here Connect with Jay on Google +


  1. Hi. I have a cal spa classic select -41. 7000 control panel. 2, motors. Pump one is two speed, which is also the circulation pump, well maybe not, seems it would then be a three speed cause it also runs for heat at slow speed. Anyway don’t see a third circulation pump. I believe I have two problems anyway. First pump 2 will only hum for maybe 5 sec. Then turn off, no pressure. Problem 2 LF low flow at certain times with no heat, and a dry warning, not sure what that means, but doesn’t sound good. The cover blew off and had a lot of leaves which I suspect maybe my LF problem. I have checked my one big filter and changed it no fix, not sure if I have another filter, better look, water level good. I am a hardcore DIY, so is it time to start taking lines apart, which will begin to teach me things, plus I assume I will have to get a new number two pump. Now one more thing the tub is 8 years old bUt last winter,Mn, I winterized it, mayBe screwed something up! Anyway not positive but possible number 2 pump never worked this year, but I think LF and dry started after leaves were in tub. Well sorry about long post any any misspelled words. Any help would be appreciated. Thanks. Bob

  2. Ok there is the small circ pump. Now all morning heat working normal. No LF or dry warnings. Number two pump still inop. But with my experience in such matters I suspect I will again see these warnings. Also last 2 things, first, when I turn one pump 2 and it hums for about 5 sec. Then turns off, could I check any other cause of this before I replace pump? And last, when I try to turn on pump 2 it starts pump one but at a level where there is no pumping action only a hum and the pump sign on panel, why is this? Thanks again. Bob

  3. Hi Karen,

    I apologize my reply did not post before and I am not sure if you received my email. This sounds like a PC board or top side control error. Try shutting off the breaker for 1 minute and turning it back on. This sometimes refreshes the pc board software if there is anything funky going on.



  4. Hi there we moved into our home last fall and a Saratoga spa excelsior came with the house. We had no issues with it until recently–I went out to check on in and the water level was extremely low with a flor message on the panel. So, I filled the tub and cleaned the filters. The Flo code was still there. I did some more troubleshooting online and found to adjust the pressure switch wheel. I did that and it didn’t seem to work either. The light did come on above the heat sign but the flo error was still there. I turned the hot ton on and off again and it was the same thing. Any ideas on what to do? Thank you soo much!!

  5. Hi Alex,

    My first question would be, did you find the source of the leak?

    As far as the pressure switch goes you may be at the point where you would want to jump out the pressure switch and see if the flo error goes away. If it does you know you need a new pressure switch.

    let me know how that works.


  6. I have a Jacuzzi Model J-280 and I get a FS2 error code on the panel when pump 1 is not running. This
    goes away sometimes and I get a solid temp reading. Any ideas??

  7. We have a vita spa. The filter is clean and both pumps run and the flo switch is new. When the pumps go off we get a FLO error. Any idea?

  8. I have a belize 3000L hot tub my error codes is LOC and FLC at the same time.I did have a flo code as well but put in a new pressure switch an that flo code is now gone and the hot tub is heating back up.the control panel on top will not let me turn the jets on or nothen.I can however turn the light on.I’m at a loss on what to do.when I turn the power on all pumps run for 30 seconds purging the system after that nothen less its heating up then the small pump turns on.shoot me a txt if you can on what to do 7852881943

  9. I have a 2000 Jaquzzi hot tub and replaced the motherboard and it worked great for a couple months. Recently the FL code came up. I noticed that the flo got weaker over a couple days. I cleaned the filter and was wondering is it possible for any debris to get past filter. Sorry for long post. Thanks Bob

  10. I have a Vita Spa. It has been set at 105° and it has been running great. After many uses, the temperature seems to go down one day, then went back into normal, 105°.

    The hot tub ran every 4 hours and after the cooling issue, it would only run for a second and turn off for a second, repeating. I turned off the GFI, waited a couple of moments, and the same thing occurred.

    Now, there is no action coming from the motor or the topside panel.

    The filters have not been cleaned in a while. I cleaned them by soaking them in muriatic acid overnight and rinsed them thoroughly.

    Once I placed the filters back in, the motor is still not turning on.

    I disconnected the topside control panel and allowed it to dry out in the sun, thinking the blank screen was due to moisture. Once I hooked the topside control panel back in, nothing displayed in the red led screen. However, there are four led lights in a square fashion that blink every 10 seconds.

    In addition, the 12VAC green led is steady and the FLASH OK green led has a steady 1-2 second flash.

    What are my options?

  11. I have an Ecco hot tub that I have drained, refilled, changed filters, and still getting FLO error. I have also tried shutting the hottub off and turning back on with out the filters installed. I believe its not a air in line issue. Is anyone familiar with this make of hottub and would you be willing to provide me some feedback on next steps. Thank you, Matt

  12. My tub is a Free Flow, I have been having LF low flow issues for some time an tub will not heat up. Filter fine, pump good, runs good no sign of air , new sensors, still get LF and sometimes sensors indicate air bubbles, heater comes on intermittently but goes out when code comes on…is it possible the PCB (board) is somehow miss reading sensor information.? I have done a lot of work and I am not able to see or find a blockage,,,,

  13. Thank you for taking the time to reply, it is appreciated.

    I have a LP warning. I have removed and cleaned the filter, just in case. I topped off the water, both were process of elimination and not required. I checked to make sure no cut valves were closed. My temp has been steady at 89, down from my usual 98. It has maintained the temp for 3 days. I ran a prime, 3 times and seems all the jets work and nothing is blocking any intake. The circ jets are pushing out luke warm water to maintain the 89. I am lost. I am out of options….I did make sure I went in to Standard mode… any suggestions? I am not near a repair place, but can have one come in…it may take a few weeks…

  14. You have checked all the easy things Derrick now it is time to check the flow sensors or pressure switch.

    You could try jumping out the leads where the pressure switch/flo-sensors plug into the board and see if the heater will click on. Or you can just order a new pressure switch (probably about $30-$50) and swap it out to see if that works. Unfortunately it is a process of elimination.


  15. So I have a 2006 artesian dove canyon spa. Over return e past few years it just seems to shut off I can’t seem to remember if it ever put out a code or what it was. I know we just recently replaced the screen cause it went out just don’t know why it keeps shutting down, to the point we have to turn off the main power and it doesn’t stay on for long anymore, any ideas on where to go from here?

  16. Jacuzzi 365. Last week FLO code. I cleaned filters, still FLO code. I ordered a new flo switch, put filters back in to wait for new switch. All of a sudden it began to to work again (going through cycles). Used hot tub tonight, ran jets, when I went to put cover back on I noticed FLO code back on. Any ideas?

  17. Hi.
    I have a hotsprings grandee and am not getting any circulation. I have changed circ pumps. And also changed sensor. (Also bought new filters) not sure where to go next? Board maybe?
    I can feel the pump running when power is on but nothing comes out in tub.When I check for flow with power off…nothing seems to be clogged. Any suggestions would be appreciated.

  18. Hi Tim,

    Sounds like a bad relay or a bad componenent IE: heater or pump. Something like this really requires a technician to come out and take a look. I be the PC board needs to be replaced.


  19. Sounds like the pressure switch sprung a leak and got the board wet. You will most likely need a new pack. But have a tech come our first to verify as that is expensive and you want to be sure.

  20. Hi. I keep getting a ohh error on my hydro pool 700 hot tub. I replaced the temp sensors but still get the error. The water is only 85f so it’s not hot. Any help would be great

  21. I have a spa in a box tub that had stopped heating. The impeller is spinning in the pump, flow into the tub seems to be pretty low. I’ve cleaned everything. If I spray into the pump with a garden hose, there is warm water entering the tub. Do I need to replace the pump? Thank you!

  22. Hi Jennie,

    I am not rally familiar with the Spa in the Box style tubs, however if you are not getting the right amount of flow from the pump into the spa, your heater is sensing that as well and protecting itself. So if the pump is weak that is your culprit.


  23. Like the rest of you I have a problem. It started with the heat element then I replaced it but the circuit board brunt up because I left it running in the rain. I have everything hooked back up the way it should be with a new board. It’s the correct board. It’s flashing a code and lighting up pump 2 light. Pump 1 is running with the heater like it should. I do hvac and I used to work for a pool and spa company. I would like to know what the board is telling me. I have a caldera spas model # DE-9800CP-DCAJ.

  24. Sorry for the delay was away for the holiday weekend.

    It could be the dip switches are not set correctly to your configuration. Make sure the dip switches on the schematic match the switches on the board.

    I am not a caldera dealer so do not know their boards. But if you can find out if it is a gecko or balboa you can find the board config settings in the manual online.


  25. I have a Jacuzzi Z112 model. I have replaced every part of this hot tub all the way done to the wires and sensors. I still have a FLO code. I replaced the mother board twice, the motor and wet end, I’ve tried 3 new flow switches, new filter, new topside control, new hot and cold sensors. I have emptied and refilled the tub through the filter. The spa runs perfect on both speeds and there is great jet action but the spa will not heat because of the FLO code. I had a mechanic come out and he was expensive and no help. Any ideas?

  26. Hi Pam,

    Does the spa have a seperate circulation pump that runs the water through the heater or does it run to one of the jet pumps? If it has a seperate circ pump than maybe that is bad?


  27. There is just one pump and it runs both speeds without issues. I am wondering if there could still be air in the lines?

  28. I have a 2010 Marquis Rondevous spa and I just replaced the impeller (after changing the water and filter). When I re-powered it, it went through it’s priming cycle, but the pump never came on. The panel showed ‘dr’ indicating no water in the heater. I bled it, and tried the pump and it seems to circulate the water, but will not cycle properly. I de-powered it, re-powered it and it still won’t cycle. It wants to – I keep hearing ‘clicking’ as if something’s trying to engage – but all that happens is that the temp indicator keeps rising to the point that the system shuts down to prevent overheating. Is the heater now engaging, but the rest of it won’t come on? I’m stumped. Thanks for any help or suggestions.

  29. Hi Phil,

    If you hear the relay kicking but the pump is not engaging the motor could be shot. If it is circulating on low speed and will not engage to high speed it could be the motor as well. Did you check the gate valves to make sure 1 of those is no partially blocking the flow, causing the DR error and the pump to over heat?


  30. I own an older Dimension One Spa from year 2000, the round model. Anyways, it worked fine, but recently I am getting a FLO error. In the past when this happened, the circulation pump still worked, it would simply turn on and off and I could re-set the flow sensor by un-plugging it from the motherboard and back and it would heat. But now I get the FLO error and the smaller circulation pump is not working. The circulation pump is only a few months old and is basically new, and I’ve already isolated it and that works fine, by un-plugging it from the motherboard and directly to 120 volts and it turned on fine right away and it circulated the water just fine, I didn’t see or feel any problem.

    So what could be the problem, is there a relay issue on the motherboard ? or something else, I’ve tired many things that are recommended and removed the filter and still the error persists.

    Any help would be appreciated.


  31. Hi Ray,

    Sounds like the board is not sending,the circ pump power. I would see if you can test the 120v at the circ pump connector. Most likely that is your issue.


  32. I have an older Coast spa.
    Ive had a Flo code on.
    I had an issue with heater element.
    I repaced it.
    Right from power up I have Flo code. I can start the pump and water circulates flo code goes off
    And temperature shows.
    After about a minute when heater when I suspect heater goes on ,
    The tub power goes down and trips the breaker.
    I can run the pump with heater dis connected and have no problem.
    Ive checked and cleaned filter.
    Checked impeller.
    No air lock.
    I am wondering if its flow sensor?
    Any suggestions appreciated
    Thanks Dan

  33. I have a reflections hot tub have filled it and bought a new filter and it is still going to flow and very cold

  34. You sure it is not air locked due to recently filling it? Is there water coming through the jets when you run the jet pumps? I am not sure if Reflections hot tubs have circ pumps or not but you could have a bad circ pump?


  35. I have Freeflow Tristar (Watkins Hotsprings). Sports series 3 person tub. Problem sounds familiar with these other posts. One pump, 2 speeds. Pump runs on low,but hums. High speeds hums loudly and trips in 10 seconds. Heating is not sufficient , heats constantly. Temp is set at 104f and shows 104f but is 100 degrees. Has flow problems etc. I have alot of experience on pumps and motors untill now. Problem started when I used a cotton oil floatie. It fibered out and I had cotton fibers in the water. I drained and change the skimmer filter twice. After a lot of search I see a screen down in the tub and they call it 303190 170 GPM suction. Can’t get it off and looks good on surface. Is this a filter or screen only. There is no water movement. I had the pump apart and impeller is clean. I put new bearings in motor and had tub drained 3 0r 4 weeks. Motor sounded great and high speed was perfect and heated good. But in 3 or4 hours , motor was noisy again etc. I wonder if this screen is clogged inside and reinflated dried cotton. Can’t find a picture or description of this suction. For the the record, tub serial is ffs3t1536. Thanks Jim

  36. Hi,
    I have a 3 year old Dynasty. I tried to go in last night and it was freezing and had the FLO code on. I powered down the breaker, that didn’t work. I just cleaned out the filters, that didn’t work. Any other suggestions that I should try before paying a tech?


  37. I have a month old jacuzzi j-470. It is connected to 60 amp so I can run everything at once. It has two jet pumps and 1 circulation pump. Just recently it keeps getting a flow switch malfunction or closed code and come on as two separate errors that read the same and disabled the heater when it does this when the one code comes on the pumps all work fine just no heat. When the two errors come on the pumps will not turn on either.
    I have reset it at the breaker and it stays off and changes nothing. The filters are clean and have no issues. I do have a scum ball in my filter box Iside the skinner bag but I don’t think this would cause an issue. The only way I get this all to clear is if I take a hose and shoot at where the heater water comes out and it immediately kicks on as normal and some days will run for a few days but lately it stays in error and after a while the pumps will kick back on but heater will not. It does. Seem like a lot of small bubbles come out when it does turn on after I use my hose trick.
    This is only a couple moth Old spa. I’m just trying to see what could be the issue and make sure maybe it isn’t something doing. It’s still under warranty so the dealer will come fix it for free but this is a pretty big issue since I like to use the spa almost everyday and have to keep resetting it. Have any ideas what this could be ?

  38. A lot of things that could be. AIr lock, clogged circ pump. Checked the filters so thats good.

    This really needs someone to look at it.

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