Mismatched Thermostats and Furnaces

Young woman changing heating
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Choosing the wrong thermostat can damage your furnace and lead to efficiency and functionality problems. Here’s a guide to help you identify and solve any furnace-thermostat problems:

Signs of a Mismatch

An under- or over-heated home or an unresponsive thermostat is a common sign of a mismatched thermostat and furnace. It’s a good idea to hire a pro to address any thermostat- or furnace-related problems.

But you can troubleshoot your thermostat and furnace prior to calling a pro. Here’s a guide to pinpointing your problem:  

Types of Thermostats

Understanding which kind of thermostat you have in your home is the first step to addressing mismatch-related issues. Here’s a look at the most common models of thermostats:  

  • Millivolt thermostats: Millivolt thermostats work best with non-powered applications like pool or Jacuzzi heaters.
  • Line-voltage thermostats: Line-voltage models are used for larger, commercial settings.
  • Low-voltage thermostats: Low-voltage thermostats are used in residential settings.

Thermometers also vary based on their functionality and energy efficiency. While the functionality of your thermostat won’t affect its compatibility with your furnace, it is an important consideration when hiring a pro or troubleshooting. Here are the different thermostat functionality options:

  • Manual/non-programmable thermostats. Manual thermostats require the user to physically change the temperature. These thermostats are less energy efficient than smart or programmable models.
  • Programmable thermostats. Programmable models automatically adjust the temperature in your home per preset levels.
  • Smart thermostats. Wi-Fi-connected thermostats allow you to adjust your home’s temperature from a smart device. Smart thermostats also track your energy usage, which helps you make smarter heating and cooling decisions.

    Common Thermostat Problems

    Problems with your thermostat or furnace can stem from a variety of malfunctions. These quick fixes will help you address issues that appear like a thermostat-furnace mismatch:

    • Problem: Flipped Breakers
    • Solution: A blown breaker can affect both your furnace and thermostat. Check your breaker box for blown fuses. Flip any tripped fuses.
    • Problem: Incorrect Settings
    • Solution: Family members, power surges and power outages can affect your thermostat’s settings. Ensure your thermostat is set to heat before making any other updates.
    • Problem: External Heat
    • Solution: Heat sources near your thermostat can affect its readings, resulting in fewer heating cycles. Be sure to place your thermostat away from fireplaces, ovens, space heaters and other sources of heat.
    • Problem: Dust Buildup.
    • Solution: A buildup of dust or dirt inside your thermostat can affect its functionality. Detach the front of your thermometer to expose the inner wires. Use a brush or vacuum to remove any dust or dirt gathering inside your thermostat.

    Common Furnace Problems

    • Problem: Dirty Filters
    • Solution: Clogged filters block air and hamper the efficiency of your furnace. Swap out your old filter with a clean replacement.
    • Problem: Faulty Electric Ignition or Pilot Light
    • Solution: Defective ignition systems limit the production of warm air. Have a professional replace any problematic pilot lights or hot surface igniters.
    • Problem: Mechanical Malfunction
    • Solution: Loud banging or scraping coming from your furnace is a sign of a mechanical issue. These can cause problems similar to a mismatch. Call a pro to address a broken or faulty furnace.

    Determining a Mismatch

    If you’re still experiencing problems, your next step is determining the source of your malfunction. Troubleshooting your thermostat will indicate whether your problem is related to a mismatched thermostat or a furnace malfunction. This test will require removing wires. Call a pro if you’re unfamiliar with thermostat wiring.

    Check for Loose Connections

    1. Turn off your thermostat and furnace. Flip off the breaker or breakers that run power to your furnace and thermostat.
    1. Remove the thermostat front. Pull the front of your thermostat toward you. This will detach the front of most models. Be sure to consult your owner’s manual before removing your thermostat’s casing.
    2. Check the wires and screws. Ensure each wire is attached to its respective mount. Next, check each screw. Tighten any loose screws or wires.
    3. Return power. Replace the thermostat case and flip the breaker or breakers back on.
    4. Run your furnace. Set your thermostat five degrees higher than your home’s current temperature. If your furnace turns on, you’ve addressed the problem.

    Test Your Thermostat

    1. Turn off your thermostat and furnace. Flip off the breaker or breakers that run power to your furnace and thermostat.
    2. Remove the thermostat front. Pull the front of your thermostat toward you. This will detach the front of most models. Be sure to consult your owner’s manual before removing the front.
    3. Locate furnace wires. Thermostat wiring is color coded. The red and white wires connect to your furnace on most models. Unscrew these wires and wrap them together.
    4. Turn the power back on. Flip your breaker. If your thermostat turns on, you have a faulty thermostat. If not, you have a furnace or electrical issue. Call a pro to diagnose the problem.