Testing a thermostat depends on whether you are checking a home HVAC unit or an automotive engine cooling system. Both can be evaluated for basic functionality using a few simple tools.
One way to check for thermostat calibration issues is to place a room thermometer a few inches from the thermostat and wait 15 minutes. The readings of both shouldn't be more than 1℉ different. If this is the case, then it's time to correct the issue.
Millivolt thermostats are typically used with a fireplace or gas-fired floor or wall heater that doesn't use electricity. Older systems with pilot lights may use millivolt controls.
To get your Lennox thermostat working again, quickly check the basics: replace the thermostat’s batteries, make sure your HVAC circuit breaker hasn't tripped, and ensure the system is set to the correct heating/cooling mode with the temperature set past the current room temperature.
Average Lifespan of a Thermostat
With a straightforward design and basic scheduling features, they are reliable workhorses that can last 10 to 15 years with proper care. Routine programming updates and occasional recalibrations go a long way toward keeping them accurate and extending their usefulness.
How can you tell if a thermostat is bad?
Disconnect the old thermostat and unscrew the mounting plate. Check the new thermostat instructions for compatibility and wiring guidance. Connect the labeled wires to the new thermostat. Attach the new mounting plate to the wall.
Depending on your specific Lennox thermostat model, the "reset button" is generally located either directly in the on-screen menu settings or as a physical switch/reboot option on the wall plate. Standard Lennox models lack a traditional, visible reset button, so you will need to perform a soft reboot or factory reset via the display.
If it doesn't start at all, you can press the button one more time. But, if you press the reset button and your furnace goes on and turns off again, don't press the button again. Continuing to press the reset button can damage your system. Doing so will pump more oil into the furnace and worsen any existing issues.
To change the batteries in a Lennox thermostat, first, locate the battery compartment usually at the back or bottom of the device. Open the compartment and replace the old batteries with new ones, observing the correct polarity.
14 Common Gas Fireplace Problems & What to Do
A plumber isn't usually needed for thermostat replacement unless your thermostat directly controls a water-based heating system, such as underfloor heating or a boiler with complex plumbing connections. Even then, an electrician is typically the right professional to handle the wiring.
Choose a Thermostat Type
Methods for Testing Your Thermostat
When your thermostat is set to 73°F but reads 78°F, your system is struggling to keep up with the heat or is misreading the ambient air. To get your home back to a comfortable temperature, you can easily troubleshoot a few common culprits.
Millivolt thermostats are the most common type used for gas fireplaces while 24 volt thermostats are common for furnaces or boilers. When the room temperature falls below the thermostat's set temperature, the IPI module triggers the gas fireplace to ignite, increasing the heat output.
The heat exchanger is often considered the most costly part of a furnace to repair or replace. It is a critical component that transfers heat from the combustion process to the air that circulates throughout your home. Over time, heat exchangers can crack due to the constant heating and cooling cycles they undergo.
To reset your furnace, turn off the power at the main breaker or emergency switch and wait 30 seconds to 5 minutes before turning it back on. This brief wait allows the electrical components to fully power down and ensures the system's computer reboots properly.
5 Warning Signs It's Time for Furnace Replacement
The way to reset a thermostat depends on its type. For programmable or smart thermostats, you usually access the factory reset or reboot options directly through the device's settings menu or by power cycling the HVAC system at the breaker for 30 seconds.
Pressing the reset button on your furnace can be safe when done properly, but it should be approached with caution. After pressing the button, give the unit a few seconds to reset and begin running again. If the furnace doesn't start up after pressing the reset button, you can try pressing it one more time.
Signs You May Need to Replace Your Thermostat
Blank or unresponsive display: A blank screen can signal dead batteries, wiring issues, or internal failure. Rising energy bills: A faulty thermostat can cause your HVAC system to run longer than necessary, driving up utility costs.
Expect to pay or charge between $150 and $450 in total for a standard thermostat replacement. This generally breaks down into $50 to $150 for the physical unit, plus $100 to $300 for a professional electrician or HVAC technician to install it.
To check if a new thermostat is compatible with your HVAC system, turn off the power to your system at the breaker, remove your current thermostat faceplate, and take a picture of the wiring. The letters beside the connected wires dictate your system's compatibility.
Yes, in many cases. If your home has low-voltage wiring and a traditional system, replacing a thermostat is very manageable with basic tools. However, smart thermostats often need a C wire for constant power, and not all homes have this built in.