How to Tell if Your Thermostat Is Failing

You can spend thousands on a new furnace or air conditioner, but they can’t function on their own. For that, you need to rely on the brains of your HVAC system: the thermostat.

It’s the device that tells the other parts of your HVAC system what to do. Cool, heat, dehumidify, humidify, etc. It’s the unit most in charge of your comfort and indoor air quality.

Like anything else in the heating and cooling industry, each generation produces models with advanced technology.

It is also one of the more troublesome devices to troubleshoot. The problem begins when your system is acting up. Maybe it’s an air conditioner that’s turning on and off frequently. Or it’s a furnace that stops working. It could be a thermostat problem, or it could be the unit itself. It might even be something as simple as a clogged furnace filter.

We’ve been in thousands of homes in Central Ohio, and oftentimes when we hear about a system that’s acting up, we check the thermostat first. Why? Because it’s easy to access, and you’d be surprised how many of them are on the wrong setting.

For instance, it might still be set to COOL in the middle of winter. It’s no wonder it’s not giving the furnace a cue to start heating. We’ve been in sweltering homes in the summer and found that the thermostat was set to ON instead of AUTO. The fan was running, but no cool air was coming out. Easy fix.

The purpose of this article is to give you a few pointers about that device on the wall that can provide total comfort in most cases, or total bafflement when things go wrong.

Three Main Types of Thermostats

•         Generally referred to as old-fashioned thermostats or non-programmable
•         Programmable
•         Smart

Read more: Nexia Thermostat Review: Benefits, Options & Price

Warning Signs That Your Thermostat Is Faulty

We present this list with a caveat: Some of the following symptoms of a broken thermostat can also be attributed to an HVAC system that’s out of whack. A furnace filter that’s too dirty can cause problems; sometimes it’s a particular piece of machinery in the furnace or the air conditioner that has worn out; the blower fan in the furnace might be too clogged with dust to function properly.

We also present this list with this thought in mind: if these things happen from day one, something is amiss with the installation, and it’s probably not caused by a bad thermostat. The symptoms below apply specifically to a device that functions fine for a while, then goes haywire.

Here are some things that MIGHT be caused by a malfunctioning thermostat.

1. Your system turns on or off frequently. The wiring inside your thermostat can become damaged, interfering with its connection to the HVAC. An HVAC technician should be able to diagnose this problem.

2. Faulty thermostat readings. When your thermostat starts to register incorrect temperatures, then it may be time to think of getting a new one. Test its reading with a portable indoor thermometer. Calibrate it (more on this later) and see if that fixes the issue. If the readings are constantly wrong after this, then the thermostat’s sensor might be malfunctioning. The issue could be old age, a manufacturing defect, or misuse.

3. Suspiciously high energy bills. The thermostat could be the culprit. If it’s not correctly reading the temperature setting, it might cause your HVAC to overwork.

4. Constant temperature swings. A failing thermostat may have a hard time maintaining settings, or it may change the temperature without warning.

5. Thermostat fails to respond to changed settings. The moment you adjust temperature settings, your thermostat should react. Typically, you’ll hear small clicking sounds when you make the changes, which will be followed by your HVAC system starting or stopping. If no changes happen after an adjustment, there could be a damaged or loose wire.

6. Your HVAC system short-cycles. Short-cycling is one of the top reasons for replacing old thermostats. The problem happens when the system shuts off earlier than appropriate, failing to complete a full cooling or heating cycle. Your home will have hot and cold spots because the fan doesn’t run long enough for the air to mix.

7. Programmable thermostats are designed to maintain settings until you reset or delete them. If your thermostat loses these settings, it could indicate a need for a replacement.

How to Troubleshoot a Failed Thermostat

•         Check the screen of the thermostat and make sure that it is lit. A blank or unlit screen could indicate a thermostat failure.
•         Many modern thermostats rely on battery power to operate. If the screen is blank or unlighted, a battery change could solve the problem. Other thermostat malfunctions could also be the result of weak batteries.
•         Double-check the settings. Make sure that the thermostat is set to provide either heating or cooling as needed, and that programmed set points are correct. Also, make certain that the temperature settings are appropriate for the season. If you have the settings too high in the summer, for example, the cooling system won’t come on and work as expected.
•         Check the circuit breakers to make sure they haven’t tripped. If they have tripped, reset them and test your thermostat and HVAC system again.

Read more: Thermostat Buying Guide

Why Do Thermostats Need to Be Calibrated?

A digital thermostat may need some sort of calibration.

Your thermostat can lose its calibration if dirt gets inside it or if it gets bumped. The result is that you may set it to 72 degrees, but it will only cool the room to 75 degrees. An incorrectly calibrated thermostat might “think” it’s running at a lower temperature than it actually is.

Three different thermostats in the same room will probably give you three different readings. Which one is correct?

The best way to find out is to set your thermostat and wait until the indoor temperature matches it. Take a glass thermometer and place it next to it. If it's more than a couple of degrees Fahrenheit different from what your thermostat shows, your thermostat may not be calibrated properly. Use that as your baseline and you can then calibrate the thermostat.

If it’s a recent model, you can access the Calibration Mode. Use your manual as your guide and check how you can enter this mode, then make the adjustment. If it’s an older model, you may need to reset it to its factory settings. A licensed HVAC technician can adjust it if necessary.

What’s the Average Lifespan of a Thermostat?

This answer can vary wildly, because it depends on a lot of factors outside an HVAC technician’s control. If a thermostat is malfunctioning after only a few years, something is obviously wrong, but even for an expert, it’s going to be hard to provide a definitive answer to this question.

Among other examples of this, we’ve seen components that are rusty and on the verge of quitting, only to discover that it’s been in that shape for five or more years, and might hold on for another 5-10 years.

However, we can say with confidence that a new thermostat “should” last at least ten years, assuming it was installed correctly. Beyond that, a thermostat could be 20 years old; that doesn’t mean it’s not good for another 5-10 years more. Factors affecting its lifespan include how well it’s installed, maintenance, and how often it’s used.

If you get a new system, we recommend having your thermostat replaced. Most people change their thermostats not out of “need,” but out of “want” or “could.”

Do you want some help in reducing your energy bills? A smart thermostat can help. Do you want to set up your thermostat so that it automatically turns down the temps as you go to work? A programmable one can do that.

Do You Always Need a New Thermostat When You Replace Your HVAC Equipment?

No, but…

A thorough HVAC technician can ensure that your thermostat is up to state and local codes. If you have one of the old-fashioned units that use mercury, it is no longer allowed. It’s legally required to install a new one if you replace your HVAC system.

Thermostat Wiring

A thermostat needs wires connecting to your furnace and air conditioner or heat pump. There is additional wiring needed depending on the complexity of the system (such as communicating HVAC units), and whether or not you have indoor air quality equipment such as humidity-control devices linked to the thermostat.

Most homes have the required wiring already set up. However, sometimes a new wire or two needs to be run between the equipment and the thermostat in order for both of them to function properly.

This generally won’t require the services of an electrician; an HVAC technician can handle it in most cases.

Where Is the Best Place for a Thermostat?

Most of a thermostat’s irregularities are based on location. Let’s say you have a thermostat on this wall, but on the other side is a refrigerator. It’s going to pick up that heat. Or it could be in the front hallway near the front door and kids are constantly coming in and out. It will pick up that cold from the outside in the winter or heat in the summer.

I’ve been in homes where the sunshine peeked through a skylight and heated the thermostat. The homeowners were baffled why the heat would kick off for an hour a day until I showed them the issue.

If it’s in a room where the door’s always closed, it won’t get a good reading. For best results, it should be on an inside wall toward the center of the house.

What Setting Should You Use: Auto or On?

Setting your thermostat’s setting to ON means the blower fan in your furnace runs, and air is constantly being pushed through your ductwork. There are advantages to this. When the air is circulating, it allows a better mix, helping to eliminate hot and cold spots. If there are rooms that don’t receive their fair share of conditioned heat or cool, having the air circulate will help.

Yet another benefit of the ON position is that air will keep circulating through the return ducts and hit the filter. This traps impurities such as dust and pollen, creating better indoor air quality and helping family members with respiratory issues breathe easier.

(We should mention that if you use this method, make sure your filter gets replaced or cleaned regularly. A clogged filter stops doing its designed job; dirty air stays dirty and crud will build up in your furnace and cause a host of problems.)

That said, leaving your fan in the ON position will likely drive higher utility bills. And you’ll have to change air filters more frequently because of the added use.

AUTO means your furnace and air conditioner will kick on according to the thermostat’s settings. Keeping your thermostat in the AUTO position means less overall energy is being used, and that can reduce your utility bill.

In the AUTO position, the air in your home won’t be as evenly distributed, which can lead to cold or hot spots versus the more even temperatures that come from letting the fan run continuously.

Many newer thermostats feature a CIRCULATE setting. This setting automatically turns fans on, running them at regular intervals without keeping them on continuously. This helps circulate fresh air without impacting your energy bills as much.

How to Diagnose Thermostat Problems in Columbus, Ohio

We try to make things easier for our customers. Fire & Ice includes a compatible thermostat free of charge with the installation of a full HVAC system.

Compared to the cost of a full system installation, it might seem like a small thing, but the more advanced thermostats can cost upwards of $500.

And if your thermostat is beyond repair, a new one can be installed at any time.

We hope you’ll give us a call or schedule a visit. Start that process below by checking to see if you’re in our service area.