Your thermostat is a tiny, sensitive nerve center for your home’s comfort. It reacts to the slightest shifts in temperature. While it has fewer moving parts than your furnace or AC unit, it can still cause headaches. If the cover is bumped or the base slips out of level, your system might simply refuse to start. Dirt is the bigger enemy here. It messes with calibration. A thermostat set to 70 degrees but actually reading 73 wastes energy. That error can bump your fuel bill up by 7 percent. You need to check your thermostat’s accuracy every year before the heating season starts.
Loose switches and corroded wires near the bimetallic element also cause failures. Tighten connections with a screwdriver. Clean corrosion with a cotton swab. But if the unit itself is drifting, you need to check calibration. Or just replace it.
How to Check Thermostat Calibration
Calibration checks are quick. They require minimal tools. Start by taping a glass tube thermometer to the wall near the thermostat. Keep it a few inches away. Pad the thermometer with a paper towel so it doesn’t touch the wall directly. Ensure neither device feels outside temperature influences. Sometimes the hole in the wall behind the unit is too big. Cold air leaks in and skews the reading.
Wait 15 minutes for the mercury to settle. Compare the thermometer reading to your thermostat’s needle. If they differ by more than a degree, dirt is likely the culprit. Remove the faceplate. It usually snaps off or uses a friction catch. Blow out the dust inside. Do not use a vacuum. The suction is too strong and might damage internal components. If you can access the contact points, rub a new dollar bill between them. The paper cleans off oxidation. Never use sandpaper or emery cloth. It ruins the contacts. If the element is coiled, use a soft brush.
If your thermostat has a mercury vial, use a level to ensure it’s straight. An unlevel unit operates incorrectly. Loosen the mounting screws. Adjust the unit until it sits perfectly flat. Tighten the screws back down.
Check the accuracy again with the glass thermometer. If it’s still off, the calibration is bad. Time to replace it.
Tools for Calibration
- Glass tube thermometer
- Tape
- Paper towel
- New dollar bill or soft brush
- Level
- Screwdriver
How to Replace a Thermostat
Replacing a faulty thermostat is straightforward if you follow the steps. You must use a replacement with the same voltage rating. It has to be compatible with your heating system.
Remove the old unit first. Take off the faceplate. Find the mounting screws. Unscrew them to release the thermostat from the wall. Remove the wires from the back by turning the connection screws counterclockwise. Be careful. Do not let loose wires fall down inside the wall cavity.
Clean the exposed wires. Scrape them with a utility knife until the metal shines. Attach these wires to the new thermostat. The electrical rating must match the old one exactly.
Once the wires are secure, push them back into the wall. Tape up the opening. This stops cold air from the walls from affecting the new unit’s readings. Install the mounting screws to secure the new thermostat. If it has a mercury tube, use a level during installation. It must be exactly level to function.
Snap the faceplate back into place. Test it. Adjust the temperature setting to make sure the heating or cooling system turns on and off.
If you followed these guidelines, you’ve maintained or replaced your thermostat successfully. The system should run efficiently now. The fuel bill might even drop. Just don’t forget to check it next year. Dust always returns.
