HVAC Thermostat Problems

Let’s discuss the most common thermostat problems and how you can avoid these unpleasant issues. 

The most common HVAC problems associated with thermostats include short cycling, incorrect readings, temperature shifts, and abnormally high bills. The majority of these issues are caused by dying batteries, dust inside the unit, and damaged wires which result in an unresponsive thermostat and, at times, a black display.

How Do You Know If Your House Thermostat Is Bad?

The great news is that if your thermostat goes bad you’re, most likely, going to notice it. Pay attention to the following signs:

  • Short cycling

When your HVAC system keeps turning on and, shortly after that, off, then the unit is short cycling. One of the reasons why that might be happening is a faulty thermostat.

Usually, damaged or frayed wires that connect the thermostat with the unit are to blame.

  • Incorrect readings

The main job of a thermostat is to keep the temperature in your house at a comfortable level.

If you have noticed that your place has become too hot or too cold, then the chances are high that there is something wrong with the thermostat

The device’s sensor can go bad due to a manufacturing defect, old age, or if you have been misusing the thermostat.

  • Abnormally high energy bills

If your energy bills have suddenly skyrocketed, then the thermostat is one of the first things that you should check.

A device that had gone bad is not able to correctly read the temperature. Usually, this fact will cause the HVAC system to overwork (and consume more power).

  • Temperature shifts

A faulty thermostat will have a hard time keeping the temperature constant. 

Try changing the setting to a very low temperature to see, if the device manages to keep up. If not – call a professional.

  • Unresponsive thermostat

As soon as you adjust the temperature settings, the device has to respond to them. If your thermostat can’t do that, then it looks like it has gone bad.

  • Thermostat’s age

A lot of thermostats last for around 10 years, but that doesn’t mean that you would have to wait for a decade before replacing the old device with a new one.

Firstly, you are going to face a lot more thermostat problems with an old device. Secondly, it might be a better decision to switch to a newer model as such devices (programmable thermostats, for example) are much more efficient. 

Read: Why Does The Room Temperature Not Match The Thermostat Setting?

How Do I Fix an Unresponsive Thermostat?

There are a few things that you can do to fix the issue:

  • Replace the batteries
  • Clean the thermostat
  • Check the wires and connections
  • Reset the thermostat

Thermostat not turning on

If your device has fresh batteries but refuses to turn on, then it might be because the inside of the thermostat is dirty.

Turn the device off and remove the cover. If the inside of the thermostat looks dusty, then use a soft brush or canned air to clean the device

You can also check the wires and the screws. Tighten the terminal screws, if they are loose.

If the wiring looks corroded, then you might have to replace the whole device.

Read: Why Does Home Thermostat Say HEAT ON But There Is No Heat?

Thermostat display not working

In the majority of cases, lack of power is the issue.

First of all, check the batteries and replace them, if there is such a need.

Tip: change the batteries at least once a year to ensure proper functioning. Also, make sure to replace them before going on a long vacation (over a month).

Secondly, check for a tripped breaker or a blown fuse. 

Finally, reset the thermostat. Simply flip the switch from ‘on’ to ‘off’, find the breaker that powers the HVAC unit and turn it off as well, wait for 30 seconds, and turn everything back on in reverse order.

How Do I Test My Thermostat?

You can test your thermostat for accuracy and test it to see if the device is even working.

  • If you’re testing your thermostat for accuracy, then you’ll need some tape, a paper towel, and a glass tube thermometer.

Choose a place a few feet away from the thermostat (make sure that it’s not in direct sunlight and is away from any heating sources). Place the paper towel against the wall and tape the thermometer over it (this will help ensure that you’re not measuring the temperature of the wall).

Leave the thermometer for around 20 minutes. After that, check the temperature difference between the thermostat’s and the thermometer’s readings.

Anything below 3 F is fine. A difference over 3 F can mean that the thermostat is dirty, unleveled, or had simply gone bad.

  • To test whether or not your thermostat is actually working, you’ll need a flathead screwdriver.

Turn the power to the HVAC unit off and unscrew the cover to expose all the wires. Take a photo of how the different wires are connected (just in case).

Unscrew and remove the wires from the terminals. If there are quite a few, remove only the red and the white one for heat and red and yellow for AC.

Twist the bare ends of these two wires together and turn the power on. If you can hear the blower turn on, then the thermostat is defective (or the wires were connected the wrong way); if the blower doesn’t go on, then you should check the continuity of the wires (there might be a break in one of them).

Also, check the wire connections and tighten the screws, if necessary.

Read: What Type Of HVAC System Do I Have?

How Long Do Home Thermostats Last?

Practically all thermostats can last for around 10 years if you manage to take proper care of the device.

The time has come to replace your thermostat, if:

  1. The thermostat doesn’t have power or isn’t responding
  2. Your HVAC system doesn’t start or is running continuously
  3. The house temperature stopped matching the thermostat setting
  4. The thermostat was placed in a room with high humidity for a prolonged period
  5. You are replacing the HVAC system

Read: Honeywell Thermostat Not Reaching Set Temperature? Here Is Why

Can I Replace Thermostat Myself?

You can attempt replacing a thermostat only if you have basic electrical knowledge and a general understanding of the device and tools that are being used.

In all the other cases, leave this job to the professional as improper installation can cause damage to the thermostat or the HVAC unit, can blow a circuit breaker, or might even result in an electric shock.

  1. Inspect the existing thermostat and its wires. If you are switching to a programmable thermostat, then you’ll need to install an additional wire.
  2. Remove the old thermostat and label the wires with a small piece of masking tape.
  3. Now you can disconnect the wires from the old thermostat. Either tape them to the wall or wrap them around a pencil.
  4. Attach the faceplate to the wall and thread the wires through the new thermostat. Connect the wires to the device by matching the letters on the thermostat and the wires.

Read: What Are HVAC Most Common Failures?

Can you replace a thermostat with any thermostat?

If you have a heat pump or central air conditioning and heating, then the chances are high that practically any smart thermostat can be integrated into the system.

However, if you have baseboard heaters, radiator heat, or swamp coolers, then a smart thermostat might not be compatible with your system.

Bear in mind that smart thermostats are only compatible with 24V HVAC systems.

Even if you think that you have found the right thermostat, you should double-check to make sure that you have enough wires (you are going to need a C-wire for the majority of smart thermostats available on the market).

In a nutshell, if you already have a smart, programmable thermostat, then you can replace it with practically any other smart device. But if you have an older model, then there are a few things that you would have to consider beforehand.