How to Tell If Your Home Thermostat Is Bad

As a Florida resident, one of the most frustrating things that can happen is to arrive home after a long day at work, only to see that your thermostat doesn’t seem to be working correctly. Is it a glitch? Is it dead batteries? Would a simple fix solve the problem, or do you have a more complicated issue in your hands? Understanding the telltale signs of a bad thermostat will help you nix worse consequences — such as an unbearably warm home in the middle of summer.

5 Signs of a Bad Thermostat

1. It’s Not Responding to Temperature Changes

This could be due to proximity to sources of heat and humidity — such as the thermostat being located on a wall that faces the exterior of your home or being too close to a room with significant temperature fluctuations, such as a bathroom, kitchen, or laundry room. Ideally, the thermostat should be installed on an interior wall, close to where you and/or your family spend the majority of the time (such as near the bedrooms or living room). An HVAC technician can make this change.

2. The AC Keeps Running Constantly

Check to see if the fan is set to on. If this is the case, the AC will continue to run even if it has reached your desired thermostat setting. While the cooling component will be shut off, the fan will continue circulating air. If the switch is set to on, change the setting to auto. If the problem is resolved with this simple fix, the thermostat is working fine. If, however, the AC continues to run without ever cycling off, the relays may be stuck together.

Relays are AC parts that open and close electrical circuits to different parts of your air conditioner. They do this automatically. However, regular wear and tear can cause them to become stuck together — preventing the thermostat from communicating with other parts of the AC. So even if you turn off the thermostat, the system will continue to run. This can only be fixed by a licensed HVAC technician.

3. The AC Won’t Turn On

A common reason for the AC not turning on is a tripped circuit breaker. Set the thermostat to off, switch the breaker to the middle setting, then to on. Then, turn the thermostat back on. If this is not the issue, turn off the thermostat again, remove the cover, and use canned compressed air to eliminate accumulated dust and grime.

Once everything is clean, inspect the wiring to see if any of them are loose. Also, check the screws to see if any of them need to be tightened. Check the inside of the thermostat for any signs of corrosion. If there is, you’ll have to replace the thermostat.
If there’s no corrosion and all components are clean and tightened, place a level above the thermostat to see if it’s been slightly moved by an accidental bump. Doing so may throw off the settings and cause the thermostat to malfunction.

4. No LED Display

There are several reasons why a thermostat’s LED display would be blank. The easier ones to resolve include an LCD brightness display that’s too low, dead batteries, or too much dirt inside the thermostat. You can troubleshoot all of these issues by reviewing the AC system’s manual. If your thermostat requires a battery, it’s good practice to always have backups, in case they run out at an inconvenient time — such as the middle of the night. If the issue is dirt inside the thermostat, you can remove the cover and clean the inside with canned compressed air.

If none of the above-mentioned solutions resolve the problem, you may have a tripped circuit breaker, a blown fuse, or a tripped float switch. Check your breaker box for the switch labeled AC. If it’s not on the on setting, switch it to the middle setting before turning it back on. To check if the issue is a blown fuse, walk outside to the condenser unit. Next to it — on the wall — there should be a small metal box. Lift the lid, take out the fuses, and test the voltage with a multimeter. If the fuse is dead, take a picture of the make and model to a hardware store to buy a replacement.

If neither of these is the problem, check the float switch. Air conditioners work by absorbing warm and humid air from inside your home, then removing the moisture from it. This condensation falls into an AC component called a drip pan. As the water level rises, it causes another component — called the float switch — to rise along with it. Once the drip pan is full, the water is siphoned out of your home through a drain line. If the drain line is clogged with mildew and sludge, the drip pan will remain full at all times. At this point, the float switch will become activated and your AC will shut off. To prevent this from happening, clean the drain line regularly.

5. The Thermostat is Old

Thermostats have a long lifespan. Typically, they should last as long as your air conditioner — which could be anywhere between 15 and 20 years, depending on how often you’ve been providing maintenance checks. If your HVAC system is approaching that timeframe, it may be time to upgrade it. This will ensure energy efficiency — since regular wear and tear may affect its accuracy when reading the temperature in your home.

Save Money on Your Electricity Bills With Complete Air Mechanical

At Complete Air Mechanical, we have experienced HVAC professionals who can ensure energy efficiency for your home or business. We provide services in Orange, Osceola, Seminole, and Volusia counties, and we offer financing options.

Call us at (407) 915-0144 and let us help you keep energy costs down.