Symptoms Of A Bad Wall Thermostat (Here Are 7 Telltale Signs)

Stacy Randall
by Stacy Randall

When the seasons shift, you remember just how critical your home’s heating and cooling systems are. Whether you’re entering a cold winter or a sweltering summer, make sure your thermostat is in good working order. The thermostat tells the HVAC system when it’s at the right temperature– but there are many ways miscommunications can happen.

If your wall thermostat goes bad, that doesn’t necessarily mean that your whole HVAC system is broken. If the system won’t turn on or off, the display is empty, or the temperature is inaccurate, do some troubleshooting. Try changing the battery, cleaning the thermostat, and verifying the settings and power source.

Thermostats should last for about ten years. Eventually, you will need to replace your thermostat. But before you call a professional repair service, do some investigating of your own.

Do You Need Your Thermostat Repaired or Reprogrammed?

Get free, zero-commitment quotes from pro contractors near you.

7 Signs That You Need a New Thermostat

While you may be able to get some use out of a failing thermostat, if the device is no longer functioning as expected, you should consider replacing it immediately. That said, here are some of the most common signs that it may be time to replace your thermostat:

1. Thermostat Doesn’t Light Up

If it looks like your thermostat is out of power, that could be a sign that the device has gone bad.

Maybe the backlight of the control panel’s display fails to light up. Or, perhaps the screen fails to show numbers when you press buttons to make adjustments. If there are issues with the thermostat’s display functions, that could signal a faulty power source or failing unit.

2. Thermostat Won’t Turn On

When you try to turn on your HVAC unit to heat or cool, does it respond? If the thermostat only responds part of the time or not at all, this may indicate a malfunction. In some cases, there might be bad wiring. Over time, wiring can fray or become worn out, causing an electrical malfunction. This malfunction can make it hard for a thermostat to gauge the temperature and respond accordingly.

3. Thermostat Won’t Turn Off

If your HVAC system continues to cycle constantly even when you tell it to stop, your thermostat may be failing.

When you change the temperature on the thermostat, it sends a signal to the machine to start or stop accordingly. If an electrical malfunction or fraying wire compromises the connection, the thermostat can’t relay messages. This can cause your HVAC system to continue cycling after it reaches the desired temperature.

4. Inconsistent Temperature

If your thermostat has trouble turning on or off, it can cause uneven heating or cooling throughout the house. This can mean that the actual room temperature doesn’t match the thermostat setting.

If the temperature varies from room to room or swings rapidly throughout the day, you may have a damaged thermostat. Sometimes these improper commands make rooms furthest away from the central HVAC less climate-controlled than rooms closer to the unit. If your thermostat is lax on relaying messages of too hot or too cold, the temperature might vary considerably.

5. Increase in Your Energy Bill

If there’s been a recent spike in your energy bill that you can’t explain, your thermostat may be to blame. Sometimes when a thermostat starts to fail, the HVAC system can’t identify when it reaches the appropriate temperature. If your unit is continuously cycling or trying too hard to heat or cool, it uses much more energy than normal.

6. Incorrect Temperature Reading

Does your thermostat say it’s 60 degrees when it really feels more like 80? It can be hard to guess the ambient temperature of a room, so use a tool to help you.

You can use a portable thermometer to verify the temperature of any room. It can even be the kind of thermometer you use outside to monitor the weather. Hold up the thermometer (or temporarily attach it to the wall) and wait 15 minutes for the most accurate results.

A discrepancy of +/- 3 degrees is considered acceptable. Anything higher or lower than that means it’s time to recalibrate, repair, or replace your thermostat.

7. Programmed Settings Disappear

If you have a programmable or smart thermostat, one telltale sign that it’s failing is it starts forgetting your settings. It’s similar to how people can begin to experience memory loss as they age. Likewise, a thermostat can start to forget dates and times when it gets old.

Wall Thermostat Troubelshooting

The Basics

This one seems like a no-brainer, but it’s worth asking the blunt question. Do you have your thermostat on the right setting?

If you’re trying to warm up your house, but you set your system to cool, your system will appear broken. And vice versa: trying to turn on the AC when the thermostat is in heat mode won’t work. Double-check that you’re in the right mode for the season before attempting any more complicated fixes.

ON versus AUTO

Is your thermostat set to “ON,” or is it set to “AUTO”? The auto setting will make the system cycle on and off as needed. You may not know if it’s working properly or not based on that behavior.

Instead, try turning the system to the “ON” position and listening for activity. Turn the desired temperature up or down a few degrees. Listen to see if the system clicks on and roars to life.

Replace the Batteries

One of the easiest fixes is replacing the thermostat’s batteries. Though, your thermostat will usually display low battery symptoms when they need to be replaced. In most cases, a low battery indicator light will appear on your thermostat, which may or may not be accompanied by a beep from the unit. You may also get a blank screen and won’t be able to turn your HVAC system on or adjust the thermostat.

Not all thermostats use batteries, but a quick change can be telling for the ones that do. If the thermostat control panel comes back to life and is responsive to commands, great. If nothing happens on the control panel with fresh batteries, you may need to call a professional. A repair or replacement may be in order.

Clean the Thermostat

If you have a mechanical thermostat with a lever on one side, there’s no battery to change. But you can disassemble and clean it to ensure nothing is getting in the way of those electrical connections. Using a can of compressed air, a soft brush, cloth, or Q-tip, gently remove dust gathered on the mechanisms.

Check the Wiring

If you have a bit of electrical know-how under your belt, check the connection of the wires inside the thermostat. Carefully disassemble it, observing the condition of the wire. Do you see any fraying or loose wires? You can also make sure that the wires are properly connected to the mounting screw.

Note: Remember to turn the power off, if possible, before poking around in electrical devices. And proceed with caution to avoid electric shock!

Reset the Circuit Breaker

Maybe your thermostat and HVAC system are having an overall power issue. Locate your circuit breaker and figure out which part governs the thermostat. Flip it off, wait a moment, and then flip it back on. It’s just like making sure a computer is plugged in before you start problem-solving why it’s “broken.” Make sure your HVAC system is getting the proper flow of electricity to function optimally.

Assess the Thermostat’s Location

If your thermostat is in direct sunlight, it will read much warmer than the house’s ambient temperature. Conversely, if it’s in a cool space like a basement, it will perceive the temperature in the house as cooler.

If you’re having trouble regulating the temperature of your home, consider relocating your thermostat. When placed in a neutral, central location, it can provide a more accurate reading.

Hire a Professional

What happens if you check off all of these troubleshooting steps and your thermostat still won’t work? If all else fails, you may need to replace your thermostat. If the thermostat is still troublesome after replacement, there may be a larger issue with the HVAC system. At this point, it’s best to call in a professional who can diagnose and fix the problem efficiently.

What Regular Maintenance Can I Do to Extend the Life of My Thermostat?

The care and keeping of your thermostat are simple. It may need to be cleaned from time to time. This helps keep dust at bay, which can compromise connections in the wiring.

You may need to change batteries or update software to keep the thermostat in good working order in newer models. The best way to keep up with preventing crashes and glitches in the system is to stay current with updates. Regularly check for any applicable updates from the manufacturer.

Calibrate your thermostat once a year. Pick a memorable occasion, like a birthday, new year, or spring cleaning, so you remember to do it annually. (You should also be checking your smoke detectors annually, so maybe this can become a package deal)!

Do You Need Your Thermostat Repaired or Reprogrammed?

Get free, zero-commitment quotes from pro contractors near you.

Related Questions

How long does a home thermostat last?

Like the rest of your home’s HVAC equipment, thermostats do not last forever. In most cases, thermostats will last around 10 years, but may last longer depending on the make, model, and type of thermostat you have. As thermostats age, they may start to malfunction as a result of normal wear and tear, rusting, wiring problems, dust accumulation, and more.Considering the fact that HVAC systems last around 15 years, the best time to purchase a new thermostat is when you replace your heating and cooling system. At this time, simply swap out your old thermostat and replace it with one that is suitable for your new system.

What are the symptoms of a bad car thermostat?

Fortunately, when a thermostat fails, this is one of the many car problems that you can diagnose and repair without the help of a professional. The most common signs that the thermostat in your car is failing is when the needle spikes and drops erratically, there’s leaking fluids in the thermostat housing, or the gauge reads high and the engine overheats.

Stacy Randall
Stacy Randall

Stacy Randall is a wife, mother, and freelance writer from NOLA that has always had a love for DIY projects, home organization, and making spaces beautiful. Together with her husband, she has been spending the last several years lovingly renovating her grandparent's former home, making it their own and learning a lot about life along the way.

More by Stacy Randall