How Does a Hot Tub Thermostat Work?

Looking for how does a hot tub thermostat works?. Great. Then you’ve to the right place. In this article, you can expect to learn the following:

  • What a hot tub thermostat
  • How does a hot tub thermostat work
  • How to calibrate a hot tub thermostat
  • How much is a thermostat for the hot tub
  • How do you change a thermostat on a hot tub

how does a hot tub thermostat work

How hot tub temperature is displayed has changed over the years. The older hot tub models have a dial thermometer to set the temperature, which often has a 5-degree variance from the temp you set and the actual temp.

On the other hand, modern hot tubs have an LCD panel with buttons, connected to the controller, to be able to raise or lower the temperature. The controller has a temperature probe that reads the water temperature.

Before we look at some of the issues that could be causing either overheating or underheating of your hot tub, let’s first look at what a thermostat is.

What is a Hot Tub Thermostat?

The hot tub thermostat is the dial or press when you want to increase or decrease the hot tub heat. Most new spas use a temp sensor connected to a circuit board and the topside control panel is used as the remote control.

Hot tubs which were made 20 years ago mostly used potentiometers and solid-state probes while hot tubs that are 30-40 years old mostly have mechanical thermostats with a capillary bulb.

Also Read:

How to heat a hot tub without a heater

How Does a Hot Tub Thermostat Work?

A thermostat is a regulating device component that senses the temperature of a physical system and performs actions so that will keep the temperature at a near desired set point.

Thermostats are used in any device or system that heats or cools to a setpoint temperature. For example, the hot tubs, air conditioners, water heaters, etc.

A thermostat operates as a “closed-loop” control device, as it seeks to reduce the error between the desired and measured temperatures.

It exerts control by switching heating or cooling devices on or off or by regulating the flow of a heat transfer fluid as needed to maintain the correct temperature.

Therefore, the hot tub thermostat is used to regulate the hot tub temperature.

As stated earlier, modern hot tubs have an LCD panel with buttons, connected to the controller, to raise or lower the temperature. The controller has a temperature probe that reads the water temperature.

On the other hand, older models have a dial thermostat to set the temperature, which often has a 5-degree temperature you set and the actual temperature.

How to Calibrate a Hot Tub Thermostat

Sometimes, if you are having issues with the hot tub heating up is because of the thermostat especially if you have the older model of the hot tub with a dial thermometer.

Generally, the newer models of hot tubs have a temperature sensor that gets inserted into a thermal well, which basically almost comes into direct contact with the water. The sensor works in conjunction with your display panel as both are connected to the control box.

There is also a high-limit sensor on the heater tube itself. However, that is designed to prevent overheating and is not directly tied to the topside panel.

With the older models, if you desire to calibrate the temperature, will mean turning the knob.

Here are some steps to follow if you have the newer model with an LCD-type panel with push buttons to set the temp.

Step 1 Check the Water, Filter, and Overall Operation of the Hot Tub

It is important to make sure there is enough water in the hot tub. Also, cross-check to be sure the filter and the jets are not clogged and are turned open.

Step 2: Check the Temperature Probe

The temperature probe is located on the underside of your hot tub. In case you are not sure of where to find it, it connects from the controller and the metal tip and gets pushed into a “thermal well”.

Make sure to push it all the way into that thermal well. Otherwise, it will not be accurate.

Step 3: Verify the Water Temperature

Set the hot tub temperature to standard 104 degrees and wait for 1 hour, assuming the hot tub was already set to at least 98 degrees.

Now, the be sure the thermostat is working properly, test the hot water with a separate thermometer.  Compare the hot tub displayed temp with the separate thermometer reading. If they do not match what’s on the thermostat, you may need to recalibrate the thermostat.

Step 4: Check the Back of the Thermostat

Most thermostats can be calibrated. If you check the back and see flat screws, then it can be calibrated. If it does not have this screw, then you need to get a professional to fix it for you.

However, for some newer models with an LCD panel and temp probe, if the probe is all the way into the thermal well, you are better off replacing it. If the problem still persists, then it’s better to replace the topside panel. Fortunately, temperature probes are quite affordable and can easily be replaced by the average homeowner.

How to Actually Calibrate a Thermostat on a Hot Tub

After you have located the thermostat, check to see if it has  Allen or flathead screw, then get the right screwdriver to turn it.

The screw needs to be turned one-quarter clockwise. Then,  depending on how far off the actual temp was from the thermometer, you wait for up to 1 hour and check the water temp again.

Keep checking the water and turning the screw one-quarter clockwise until the water temperature matches the therm

When they match, your hot tub thermostat will be calibrated, and your hot tub is ready for use.

If after this, they do not match, and the issue still remains, then you may need to replace the thermostat completely.

hot tub thermostat troubleshooting

How to Change a Thermostat on a Hot Tub

If after the calibration, you realized that you need to change the thermostat, you will need to follow these steps to make it happen.

  1. Turn of the power at the disconnect box near the hot tub.
  2. Remove the main panel from your hot tub.
  3. Locate the thermostat.
  4. Disconnect the wires from it to both the control box and any temperature probes.
  5. Remove the thermostat. You may need to remove some screws, otherwise, it can easily be pulled off.
  6. Replace with the new thermostat.
  7. Then screw the thermostat back in or push it back in.
  8. Close up the panel where the thermostat is located
  9. Turn the power back on.

If after changing the thermostat, the problem still persists, then you need to test the hot tub temperature sensor. The steps are covered below.

How to Test a Hot Tub Temperature Sensor?: Hot Tub Temperature Sensor Troubleshooting

Most temperature sensors have a resistance of 10,000 at 77-degrees Fahrenheit.

However, the colder the water the higher the readings are up to 50,000, whereas warmer water at 100-degrees Fahrenheit will produce much lower readings.

This should be indicated in the booklet the manufacturer provided you with. if you end up with a zero reading, then the issue is with the temperature sensor, or the cable is damaged.

Here is how to test a hot tub’s temperature sensor:

  • Shut off the hot tub’s power at the disconnect panel
  • Set the Ohm meter to 20,000
  • Find the end of the sensor wire
  • Unplug the sensor wire from the control box
  • Next, place the leads of your Ohm meter onto the red & green wires
  • Compare the readings to a Thermistor Resistance vs. Temperature Chart from your hot tub manufacturer

How Much Does a Hot Tub Thermostat Cost

Running a hot tub is already a costly business!. But, we’ve got to pay for that luxury. Replacing damaged parts can also come at a high cost sometimes depending on whatever it is that needs to be replaced.

One of those components that sometimes needs to be replaced is the thermostat.

The cost of a  thermostat replacement for a hot tub will vary on the type of model of the hot tub that you own.

But the costs of a thermostat range from anywhere from $25  to $150, depending on the hot tub itself. But you can get a high-quality one for under $100 online.

However, as I mentioned earlier, the model you have will determine the cost. Mostly, high-end hot tubs also have expensive parts. Also, the older models that have hard-to-find parts can be expensive as well.

Final Thoughts on How Hot Tub Thermostat Works

A working thermostat is good to get the hot tub temperature correctly. This article has outlined how you can calibrate the thermostat or temperature sensor correctly.

Once you realize it’s a faulty thermostat, then you can go to work and get it fixed. If it is beyond you, then you will need a professional to fix it for you.

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