How to Troubleshoot a Lux Thermostat

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Lux has been making thermostats since 1914 and prides itself on innovation and reliability, but sometimes, a Lux thermostat stops working correctly. Knowing how to troubleshoot a Lux thermostat can help you get yours back on track when it's a minor issue. Troubleshooting can also help you decide if you need to contact your HVAC service company when the basic checks don't fix the issue.


Check the Batteries

Many Lux thermostats operate using AA batteries, so you'll need to replace the batteries occasionally. Lux recommends Duracell or Energizer batteries for the thermostats. Low batteries can result in a blank or fading display. They can also cause the thermostat to heat or cool to the wrong temperature. Some Lux thermostats also have a low-battery indicator on the display.


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When replacing the batteries, use a pencil eraser to clean the contacts. Ensure you install the batteries in the correct direction using the + and - signs on the thermostat as a guide. Check the spring contact to make sure it's firmly connected. Turn the thermostat back on and give it several minutes to see if the HVAC system turns back on.

Check Power Sources

Another troubleshooting technique to try is checking the power source for the HVAC system. If your furnace or air conditioner isn't getting power, the thermostat can't turn it on. Check the circuit breakers for the HVAC system. If they're off, turn them back on and give the system several minutes to start working.


Also, check the furnace switch, which you can usually find on the unit or the wall nearby. It looks like a regular light switch, so it's easy to flip it off accidentally. Flip it to the "on" position if it's off and give the system time to start.

Verify the Settings

Sometimes, what you think is an error with the thermostat is just a settings mistake. Verify that your Lux thermometer is set to either "heat" or "cool" depending on which part of the HVAC system you're trying to use. Check the temperature of the room compared to the temperature you have set. The thermostat will only turn on the HVAC system if it needs to heat or cool to reach the temperature setting. For example, if the room is already cooler than the 72 degrees Fahrenheit you've chosen for the setting, then the air conditioning won't turn on until the room warms up.


If your fan runs constantly, check the fan setting. You can choose between "on," which keeps the fan running constantly, and "auto," which only runs the fan when the HVAC system runs. Choose the "auto" setting to stop the fan from running constantly.

Inspect the Wiring

A Lux thermostat wiring issue can keep it from working properly. Shut off the power to the thermostat at the breaker and pull the cover off your Lux thermostat to reveal the wiring. Make sure everything is connected to the terminals properly. If the Lux thermostat is newly installed, there could be mistakes in how you wired it.


Refer to the wiring diagram in the manual for your specific Lux thermostat. Lux thermostats can range from two to seven wires depending on the type of thermostat and heating and cooling system, so the wiring can vary. Low-voltage Lux thermostats shouldn't be connected to line voltage. When installing a new thermostat, it's important to note the terminal letter for the previous wiring rather than just matching the wiring color. If you're not sure if the thermostat is wired correctly, contact an HVAC professional to check the installation.



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