There have been more than 30 million units of smart thermostats sold in the USA since the first smart thermostat has been available in the marketplace. Millions of these units are currently still in use, with probably the most of them in home HVAC systems. Unfortunately, thermostats sometimes stop working or encounter other problems. Homeowners have two main questions. The one question is whether there are common problems causing thermostats not to work or do different brands encounter different problems. The second question is whether the issues can be solved in a DIY manner or do you have to get a professional to attend to the problems.  

Most thermostats stop working or encounter problems because of common problems such as loose connections and low batteries. But there are also a few problems that are unique to specific brands or are more frequently experienced with specific brands. Fortunately, most of the problems can be resolved without calling a professional.   

In this article, we’ll first look at common thermostat-related problems and possible solutions, and then we’ll discuss a few problems that are to a certain extent brand-related. 

Common thermostat problems – all brands

Before we look at specific brands’ “unique” problems, let’s discuss four common problems that may occur in any brand.

Problem 1: Thermostat not working at all

If your thermostat is not working at all, it can be due to old age and has to be replaced. But there may be other common reasons why the thermostat doesn’t work. Let’s look at some of the reasons: 

No power is going to the thermostat

When no power is received by the thermostat it stops working. This loss of power could be caused by a poor connection, dead batteries, a blown fuse, or a tripped circuit breaker. Thus, before you call an HVAC professional or purchase a new thermostat, check all of these aspects. Check by following an eliminating procedure, starting with what seems to you the easiest to check. 

Loose wiring

Loose wiring can also be the reason why your thermostat doesn’t work. Open your thermostat and examine the inside. Check for any loose wiring and fastened all connections. 

If you don’t see any problem, the best is to call your HVAC professional.  

Problem 2: Thermostat won’t allow manual changing of temperature

On some occasions, a thermostat doesn’t allow you to change the temperature. This is a very annoying issue. Some reasons why this is happening include the following:

The thermostat unit is locked

Most digital thermostats have a lock feature to allow homeowners to prevent others from making adjustments to the temperature. If your thermostat is not allowing you to change the temperature, the lock feature is most probably enabled. 

Check your settings and ensure that the lock feature is not enabled. 

The thermostat is in auto mode

Generally, when thermostats are in auto mode, they won’t allow you to change the temperature manually. The unit will only work according to the settings and programming you’ve provided. 

If you want to adjust the temperature manually, you’ll have to change the mode of the unit to either Heat or Cool/AC.

Problem 3: Thermostat not reaching a set temperature 

If you’re experiencing that your home is constantly not reaching the set temperature, you might have a thermostat that doesn’t reach the proper temperature anymore. This may be caused by any of the following:

Broken or damaged sensors

Thermostats need multiple sensors to work effectively. Your thermostat will not be able to control the temperature in your home with broken or damaged sensors. Broken sensors normally result in temperature readings that are higher or lower than what you initially set the thermostat to.

Unfortunately, fixing a damaged sensor is usually not a DIY job. Contact an HVAC professional if you think there is a problem with one or more sensors. It may be necessary to replace the thermostat. 

Incorrect thermostat location

If your thermostat is, for instance, located near either a very warm place like a fireplace, or a cold area in your home, it might lead to incorrect temperature readings. The thermostat may register a reading that is far higher or lower than the rest of your home.

To rectify this problem, move your thermostat to a more “neutral” place in your home. Sometimes it is a good idea to move the sensor to the room where you and your family are most of the time, like your TV room. 

Dirty thermostat

A thermostat unit needs to be clean to work effectively. You have to clean the unit frequently as dust, dirt, and lint particles can get inside your unit over time. The dirt can block the sensors or cause other issues that can result in an incorrect temperature reading.

To clean the thermostat remove the thermostat cover and use a soft tip brush or cloth to wipe away dirt and other particles. Ensure that you don’t “disturb” any wire connections.


If corrosion has taken place in your thermostat unit, the electrical components might be affected. This problem can be rectified by using an electronic contact cleaner. 

If you have an older thermostat, you could encounter problems removing the corrosion and will it perhaps be better to replace it.

Problem 4: Frequent short cycling or continuous running

The most common reason why you experience frequent short cycling or continuous running of the system is that the thermostat doesn’t sit level or is dirty inside.  You can easily rectify the problem by opening and cleaning the thermostat from any dust and dirt, and then levelling it again. 

Common problems with Nest thermostats

The following are some of the most common Nest thermostat-related problems that you can encounter: 

Problem 1-Nest: The vents release hot air instead of cold air

When your vents are blowing hot air instead of cold air, after you’ve installed your new Nest thermostat, the cause is most probably improper wiring. You’ve probably followed the conventional wiring of your old thermostat instead of using the heat pump row.

This problem can easily be fixed by relabeling the wiring and correctly using the heat pump side. After you’ve wired the thermostat correctly, the Nest thermostat will detect it, and you will feel the cool air from your vents.

Problem 2-Nest: There is no power to the “Rh” wire

You will know there is no power to the Rh wire when your system is not coming on and you receive an E74 report. 

To rectify the problem, check whether one of the circuit breakers has tripped. If so, switch the breaker off and on, and check if your system is powered. If the system still doesn’t work, there might be poorly connected Rc and Rh wires. 

Check the connections and fastened them securely. If there is only one wire to connect to the thermostat, it should be connected to the Rh port. If all the connections are correct and the system is still not coming on, check if you perhaps have a blown fuse. If so, replace it and your system will work again.

Problem3-Nest: Low battery

There might be battery problems if your Nest thermostat has difficulties connecting to the Wi-Fi and thus causing the thermostat to stop functioning. The first thing to do is to check the battery’s status. Go to “Settings” and scroll to “Technical info.”  Your battery level should be above 3.6Va and the line level should ideally be above 20 mA. 

To solve the problem you have to charge the battery. There are three possible ways to do so:  

  • Charge the thermostat with a USB cable.  
  • Use a 24V common wire transformer. 
  • Remove the G wire and put it in the C terminal.

If the battery doesn’t’ charge, you’ll have to replace the battery.

Problem 4-Nest: The thermostat keeps on blinking and is unresponsive

Usually, a blinking green light is an indication that the thermostat is undergoing a software update. This lasts only a few minutes and then the thermostat should restart immediately. If the green light keeps on blinking and the thermostat stays non-responsive, the system may have frozen.

To get it working again, remove the thermostat from the base, and then put it back again. The reconnecting display should then come on, and if it doesn’t, press the thermostat for a few seconds to restart it.

If you are interested, here is a detailed article on this: Nest thermostat blinking: Reasons and fix

Problem 5-Nest: The thermostat keeps turning on and off

If your Nest thermostat keeps turning on and off it is possible that your HVAC system has a problem, and not necessarily the thermostat. A clogged air filter, for instance, can cause your air conditioning system to shut down. Then your Nest thermostat will not be able to draw power to charge its battery. This will cause the thermostat to destabilize.

Checking of your HVAC system is unfortunately not an easy DIY job and the best is to call a professional to search for the problem.

Common problems with Honeywell thermostats

The most common problems relating to the Honeywell thermostats are the following:

Problem 1-Honeywell: The display screen is blank

Although a blank screen might sometimes indicate that you need to buy a new thermostat, there are also other reasons why the screen stays blank. First, follow the following steps to see whether you can rectify the problem before you purchase a new thermostat. 

If you have a programmable thermostat, the problem can in most cases be solved by replacing the batteries.  If it is still blank after you’ve inserted new batteries, there could be a problem with the wiring. Ensure that all the connections have been done correctly and that all of them are still firmly connected. 

If the problem is not solved, check whether the power is flowing for your furnace or air handler. Ensure that the switch close to the indoor unit is switched “up.” Also, make sure all furnace cabinets or air handler doors and panels are tightly in place.

Problem 2-Honeywell: The HVAC system won’t work

When your whole HVAC system is not working, your first step is to make sure that your thermostat is switched to “cool” or “heat,” and not to “off.”

Also, ensure that in the summer the thermostat is set beneath the ambient temperature, and in winter, higher. 

If the equipment still doesn’t start, check that the circuit breakers are all on. If the problem persists you’ll have to call an HVAC professional to check the whole system.

Problem 3-Honeywell: “Cool On” or “Heat On” is blinking

Start by ensuring that the thermostat is securely switched to either “cool” or “heat.” You’ll know whether the thermostat is telling the right system to run by checking whether either “cool on,” or “heat on” is shown. 

If that is the case, you normally don’t have to worry any further, as your thermostat is in a five-minute delay state. This is a feature that stops your unit to prevent damaging short cycling after you’ve lost power and it has come back on again.  

If the thermostat keeps on blinking the best is to contact your HVAC professional.

If you are interested in knowing more, here is a detailed article on this: Honeywell thermostat cool on light blinking: Fix

Common problems with Ecobee thermostats

Problem 1 Ecobee: Ecobee temperature reading is incorrect

A common Ecobee issue is that the thermostat does not show an accurate temperature reading. If this is the problem you’re encountering, try the following:

Reset the thermostat

In most cases, you only have to restart your thermostat to get rid of the problem. To reset the Ecobee thermostat go to the thermostat screen, and go to “Main Menu,” then to “Settings,” and “Reset”  and press “Reset all.” This will return your Ecobee thermostat to factory settings and all your settings will be deleted. Once the reset is done you have to re-setup your Ecobee from scratch.

Resetting ecobee thermostat

Make a temperature correction

If the thermostat is still showing the incorrect temperature, go into the settings and set an offset temperature correction. This function can be used to modify the thermostat sensor reading “sensitivity variance” and then permanently correct it by up to 10 degrees in either direction.

Check for cold air behind the thermostat

Make sure the hole in the wall is filled so that you are not getting cool air blowing onto the thermostat. If there is a hole, you can rectify it by fixing the hole with an outlet sealer. It is quick to apply and is better than clay or putty.

Move the temperature sensor

Incorrect temperature readings can sometimes be caused by obstacles in the way of the thermostat’s sensors. It can be items like furniture or curtains that are blocking the sensors. Make sure there aren’t any obstacles in the way of the sensors.

You can also move the thermostat to another location. 

Problem 2-Ecobee: Thermostat calibrating for too long

To properly read the temperature inside your home, the Ecobee thermostat calibrates on the first installation. Then it usually only calibrates when you have had a power outage, intentionally rebooted the thermostat or changed some of the thresholds. The calibration should not take longer than about 20 minutes. 

If you see the “Ecobee Calibrating” message for more than 20 minutes, there might be an error. Try to reboot the thermostat by removing it from the wall and replacing it again. Wait for 20 minutes and if it then stops calibrating, you’ve resolved the issue. 

If the problem persists, check for firmware updates by going to “Main Menu,” “About,” and then “Version.” Compare the version with the latest version on the Ecobee support site. By updating the firmware the problem may be solved.

Problem 3-Ecobee: Wi-Fi sensor connection issues

A common problem you might experience with your Ecobee thermostat is a connection issue with the remote sensors. 

If you are experiencing this problem, first see whether the issue can be resolved by moving the remote sensors closer to your Ecobee thermostat. If the problem persists, you might have a Wi-Fi problem.

Here are some things to do to try and rectify the problem:

Check whether the router uses a 2.4 GHz network

If you have a dual-band router, connect to the 2.4 GHz band rather than the 5GHz band. Only the Smart Thermostat with Voice Control is dual-band compatible.

Check whether the thermostat’s firmware is up to date

To check for firmware updates go to “Main Menu,” “About,” and then “Version.” Compare the version with the latest version on the Ecobee support site and download the latest version if necessary.

Check the Wi-Fi signal strength

Check the signal strength on the Ecobee by going to “Main Menu,” “About,“ and “Wi-Fi.” A signal strength lower than 75% might cause connection issues. Attend to your Wi-Fi installation to get the strength above 75%.  


Because all thermostats have the basic function of managing the temperature in people’s homes, it is easy to understand that they can encounter common problems. In this article, we’ve highlighted some of the common reasons why thermostats stop working effectively and offered possible solutions. We’ve also looked at possible solutions for brand-unique problems. We hope that this information will help you to resolve most of the issues you may encounter with your thermostat without calling your HVAC professional.


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