If your hot tub suddenly shuts off and flashes an error like **“HL,” “OH,” or “HOT”**, your high-limit switch is trying to tell you something important — the water is too hot or the heater is running without enough flow.
Safety Notice: This article is for general informational purposes only. Pools, spas, and hot tubs involve electricity, heat, water, and chemicals that can be dangerous if handled improperly. Always follow manufacturer instructions and safety guidelines. If you are unsure or uncomfortable performing any repair, consult a qualified pool or spa professional
This guide will explain what the high-limit switch does, common causes of these errors, and simple steps you can take to get your spa safely running again.
To get a more general idea as to why your hot tub isn’t heating visit here: Hot Tub Isn’t Heating, causes, tests and what to check
What Is a High-Limit Switch?
The high-limit switch is a safety device that monitors your spa’s temperature. It automatically shuts off the heater if the water temperature rises above a safe limit (usually around 118–120°F or 47–49°C)./ This prevents overheating, which could damage the heater, or pose a safety hazard.
If your tub shuts down and you see an error code like: HL, OH, OHH. HOT, Heater tripped or “Overheat” warning. it means the high-limit switch has detected temperatures that are too high — or it *thinks* they are.
Very First Thing To Check:
Usually the first thing I would ask a customer to do when they called with a high limit issue, was to completely remove the heater. I would then ask them to reset the breaker by turning it all the way off, wait for about 30 seconds then turn it back on. About 80% of the time the customer would call me back to let me know that their spa is now heating properly. This is due to high limit issues being caused by poor water flow due to a clogged filter.
–Common Causes of High-Limit Trips
Please note that on most Spas you need to reset the breaker (turn the breaker off then back on) to clear the error
1. Poor Water Flow
If water isn’t moving properly through the heater, it can overheat quickly.
* Make sure your filter is clean
* Check that the water level is above the jets
* Confirm the circulation pump is working and there are no airlocks.
Often, clearing a flow problem will reset the high-limit error after resetting the breaker
2. Dirty or Blocked Filter
A clogged filter restricts circulation, which can cause the heater chamber to overheat.
Turn the breaker off, Remove the filter, then turn the breaker back on. Run the tub for a minute without it. If the error clears, clean or replace the filter.
3. Temperature Sensor or High-Limit Sensor Failure
Sometimes the problem isn’t the temperature — it’s the sensor reading it wrong.
* Inspect the sensor for corrosion or damage.
* If the spa consistently trips even at normal water temperatures, the sensor may need replacing.
You may need a technician to test or replace the sensor safely.
4. Stuck Heater Relay or Malfunctioning Control Board
If the relay that controls your heater gets stuck, it might keep heating even when it shouldn’t.
* Turn off power to the spa immediately.
* If the water keeps heating after power is restored, contact a professional to inspect the circuit board.
5. Excessive Ambient Heat or Sunlight
In hot summer weather, the sun alone can push your spa’s temperature over the limit — especially with the cover on.
* Prop the cover open slightly to release heat.
* Set the spa to “economy” mode during heat waves.
6. Your heater element is touching the side of the heater tube
This will cause your heater tube to ger hotter than it should
How to Reset a High-Limit Switch
Some older hot tubs have a manual reset button on the heater tube (a small red button you can press).
Steps to reset:
1. Turn off power at the breaker.
2. Let the water cool down below 100°F (38°C).
3. Press the high-limit reset button (if your spa has one).
4. Restore power and monitor the temperature.
If the switch keeps tripping, there’s still an underlying issue that needs fixing.
However, most Spas now don’t have a reset button. To get rid of the message you need to turn the power to the spa off then back on.
Preventing High-Limit Problems
* Keep your filter clean and replace it regularly.
* Maintain proper water level and flow
* Keep your heater and pump area free of debris for good ventilation.
* Check water temperature occasionally with a separate thermometer to verify your spa’s reading.
A high-limit error is your hot tub’s way of keeping you safe. While it might interrupt your soak, it’s preventing potential damage to your heater and electronics.
Most of the time, these issues come down to low flow, a dirty filter, — simple fixes you can handle at home.
If your spa keeps shutting down even after cleaning and resetting, it’s time to call in a professional technician. Catching and fixing the problem early can save you from costly repairs later on.
Related Articles:
Written by Dan Harvickson, pool & spa repair technician.