Hot Tub Won't Heat?! Troubleshooting Common Hot Tub Heater Problems (2023)

Hot tubs are a wonderful way to relax and unwind, but when the heater isn't working properly, it can put a damper on your experience. A hot tub without heat is essentially just a small pool, and that's not what you signed up for. In this article, we will explore the top five hot tub heater problems and provide you with troubleshooting tips to help you get your hot tub back to its intended purpose of being hot and inviting.

1. Low Flow

One of the most common reasons why your hot tub may not be heating properly is low flow. Sufficient water flow is crucial for the hot tub heater to work effectively. If you notice that your hot tub isn't heating up as it should, the first thing you should check is the water flow.

Troubleshooting Low Flow:

  • Clean the Spa Filter: Low flow is often associated with a dirty spa filter. Remove and clean the filter(s) to rule out any pressure or flow rate problems.
  • Check for Clogs: Low water level, a clogged pump impeller, closed valves, clogged pipes, or blocked spa drain covers can also cause flow issues. Inspect these areas and clear any obstructions that you find.
  • Inspect the Inlet Screens: Some hot tub heaters have screens on the inlet side to trap debris. If these screens become clogged, it can reduce water flow. Clean or replace the screens as needed.

If these steps don't resolve the low flow issue, it's possible that the problem lies with the pressure switch or flow switch.

Pressure Switch: A pressure switch is screwed into the heater chamber and senses when the water pressure is too low. It protects the heater against overheating by breaking the electrical circuit powering the heater element. You can test the performance of most pressure switches by using a jumper wire to connect the two wires together, bypassing the switch. Some pressure switches can be adjusted with a thumb wheel or small slotted screw to close the circuit at a particular pressure rating.

Flow Switch: Some hot tub heaters use a flow switch instead of a pressure switch, or sometimes both devices in combination. Flow switches are triggered by water flow and close the circuit when the flow is sufficient. You can test the performance of most flow switches by using a jumper wire to connect the two wires together, bypassing the switch. Ensure that the surfaces are clean and free of scale, and that the paddles are not bent.

2. Thermostat Issues

The thermostat is responsible for regulating the temperature of the hot tub water. If you're experiencing issues with the temperature, the thermostat could be the culprit.

Testing the Thermostat:

  • Older Spas: For older spas, check the thermostat "knob" to see if it's faulty internally or if the sensor bulb has become corroded. Test the thermostat using a multimeter set on ohms (Ω) to measure resistance.
  • Newer Spas: For newer spas with a topside control panel, the thermostat is usually replaced by a temperature sensor. Inspect the cord and probe for damage, and ensure that it is plugged into the panel securely. If the topside control panel is displaying incorrect water temperature or appears to be water damaged, it could be an issue with the control panel itself.

3. High Limit Switch

The high limit switch is an important safety feature that prevents the hot tub heater from overheating. If the high limit switch is faulty, it can cause the heater to shut off prematurely or not heat up at all.

Troubleshooting the High Limit Switch:

  • Check for Error Codes: High limit errors will often display as an HL code or OH code on the control panel when they are the cause of the heater problem. On older spas, the red button on the device will physically "pop out" when the high limit has been reached.
  • Inspect for Issues: Nuisance high limit tripping can be related to low water flow, incorrect voltage, a malfunctioning element, loose wire connections, damaged wires, or a faulty high limit switch. Ensure that all connections are tight and not oxidized, and inspect the high limit switch for any signs of damage or malfunction.

4. Hot Tub Heater Element

The hot tub heater element is responsible for heating the water. If the element is faulty or damaged, it can result in low or no heat in your hot tub.

Testing the Heater Element:

  • Resistance Test: Use a test meter set on ohms (Ω) to measure the resistance of the spa heater element. A good element should usually display 9-12 ohms. If the resistance pegs to "infinity" or keeps rising slowly, there is a short in the element and it should be replaced.
  • Inspect for Scale Buildup: Heater elements can develop scale buildup from hard water or saltwater sanitation systems. If the outer casing of the element becomes cracked, a new element is needed. Using a sequestering agent and maintaining proper water chemistry can help reduce scale formation on heater elements.

5. Other Causes of Hot Tub Heater Problems

In addition to the common hot tub heater problems mentioned above, there are a few other factors that can affect the heating performance of your hot tub.

GFCI Tripped: Check the electrical outlet on your spa pack for a tripped GFCI. If the red TEST button is popped out, push it back in firmly.

Door Interlock Open: Some spas have a cabinet switch or spa pack cover switch that prevents operation unless the doors are tightly closed. Ensure that all doors are securely closed.

Spa Cover Needs Replacement: Warped, broken, or ill-fitting spa covers can allow heat to escape, reducing the effectiveness of the heater. Consider replacing the spa cover if it is in poor condition.

Loose Wires: Check all wire connections to ensure they are tight and not oxidized. Chewed wires, melted wires, or crimped wires can also cause issues and should be addressed.

Blown Fuse: A power spike, surge, or incorrect voltage may have blown a fuse on the control board. Check the fuse and replace it if necessary.

By troubleshooting these common hot tub heater problems, you can often identify and resolve the issue without the need for professional assistance. However, if you're unsure or uncomfortable with performing these troubleshooting steps, it's always best to consult a trained hot tub technician for assistance.

Remember, proper maintenance and regular servicing of your hot tub can help prevent many of these issues from occurring in the first place. Regularly cleaning the spa filter, maintaining proper water chemistry, and following the manufacturer's guidelines for maintenance and care will go a long way in ensuring your hot tub heater operates efficiently and effectively.

If you're still experiencing hot tub heater problems or need further assistance, don't hesitate to reach out to the team of experts at Leslie's. Their trained service staff can help you navigate through any hot tub challenge you may face and get your hot tub back to its optimal performance.


A hot tub without heat is a disappointment, but with the right troubleshooting steps, you can often identify and resolve common hot tub heater problems. By addressing issues such as low flow, thermostat problems, high limit switch malfunctions, heater element failures, and other potential causes, you can restore your hot tub to its intended purpose of providing a warm and relaxing experience. Remember to prioritize regular maintenance and seek professional assistance when needed to ensure the longevity and performance of your hot tub heater.

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