Why Does Your Thermostat Have No Power? (Fix It Now!)

It can be frustrating when your thermostat display is blank, or the device is non-responsive. The thermostat controls your home’s temperature, whether it’s heat or air conditioning. An uncomfortable home is something no one wants. 

When a thermostat has no power, this could be due to the breaker being off, loose wires, an overheating device, a blown fuse, a dead battery, or the safety switch being triggered. These can be fixed by resetting the breaker, replacing the fuse, securing the wires, and replacing the battery. 

Broken Thermostat

However, this is only the tip of the iceberg. Depending on the underlying issue, there are several ways to restore power to your thermostat. Keep reading to learn about these solutions, how to apply a fix and when to consult a professional for help. 

Common Reasons Your Thermostat Doesn’t Have Power

There are several reasons your thermostat does not have power. Luckily, you can resolve many of these issues quickly and without the help of a professional. Here is an overview of the most common reason and how to troubleshoot the problem. 

The Breaker is Off 

The circuit breaker is the control center for the electrical system. It is a critical safety device that helps prevent power overloads and other electrical issues. It functions by tripping the circuit, thus cutting power to the area. 

This often occurs when too much electricity is present, and the circuit heats up. For example, if your thermostat is connected to a circuit breaker that has been tripped, it will not receive any power. 

Turning Off the Breaker
The Breaker is Off 

The breaker box is often found in hidden locations like a closet, the basement, the garage, or a central area like the hallway. It is typically encased in a metal box with a small hinged door set into the wall. 

Once the breaker box has been located, it is important to know what switch controls which circuit. Most breaker boxes will have small labels next to each switch with a short description of the area the circuit controls. However, it can be tricky to isolate the correct switch if they aren’t labeled. In this case, turn on all the lights and flip each switch to see which lights go out. 

The Wires Are Loose 

Loose wires are a common issue with electrical equipment. This can occur when the writing that runs to the panel box becomes detached or faulty. To check for this issue, remove the panel from the front of the device. Remember to flip the switch on the breaker to ensure you do not receive a shock from the device. Next, take a look at the wires connected to the panel. Notice any wires that look looser than the other or even completely disconnected. If all wires are attached, take a closer look for any damage to the wires, this can be rust, corrosion, or cuts in the sleeve. If you notice any of these issues, the wires could be the cause of the issue.

Loosen Wires

The Unit Overheated 

Overheating is another issue that can cause your thermostat (such as the Ecobee or Carrier unit) to lose power. If the unit is hot to the touch, it may have overheated. This can be caused by the device being old. Consider how old the thermostat is; if it is more than ten years old, the device can overheat when it is time to replace it. 

Another reason the thermostat can overheat is dust and dirt. Check under the cover for residue covering the unit and preventing heat from escaping when it is in use. Thermostats need to be kept clean to ensure they work correctly. In addition to overheating, this can cause incorrect temperatures to display increasing energy costs. 

A Fuse is Blown

Similar to the issue with the circuit breaker being tripped, a blown fuse can cause a thermostat to have no power. This fuse is located in the furnace itself. Most newer furnaces will have a fuse to prevent any electrical overloads from damaging the unit. Often this overload is not enough to trip the circuit breaker, which is why the fuse is vital. It will prevent any fires caused by the overload. 

You can find this fuse behind the main electrical service panel. If it is not here, look for another panel or check the furnace house. If you have trouble finding it, the owner’s manual will provide the location of the fuses. 

Once the fuse is found, look at the middle of it; if the small metal bar connecting both sides of the fuse is broken, the fuse has been blown and will need to be replaced. 

The Battery is Dead

Even with newer thermostats being controlled via Wi-Fi and wired into the home (l, batteries are still important to ensure the device runs as it should. The battery saves programmed settings saved on the device in the event of a power outage. It can also help keep the temperature of your home stable if the power is out. 

Battery of Thermostat

The battery is easy to find behind the front panel of the thermostat. Once the panel is removed, look for a small round lithium battery, typically CR2032, or alkaline batteries, normally AA or AAA. 

The batteries in a thermostat will often last from eight months to a couple of years, depending on how often power is drawn from it. Most modern thermostats will have a low battery icon on the digital display, giving you a heads-up on when to replace it. 

The Safety Switch is On 

Many newer HVAC systems will have a safety switch to prevent damage and fires. If this switch has been triggered, this can cause the thermostat to shut off and display a blank screen. It can go off if the temperature of the HVAC unit is too high and the condensation overflow pan is too full.

Depending on the unit’s orientation, you can find the switch in different locations. On vertical ACs, it is typically mounted on the front near the main drain. The switch will be on the emergency drain pan under the air handler on horizontal units.

It is important to note this isn’t a simple on/off switch. The excess water will need to be removed for the safety switch to turn off. 

How To Fix a Thermostat With No Power

Now that you know what can cause a lack of power to a thermostat, it is time to fix the problem. Rest assured, this is a common issue and can often be resolved without the help of a professional. Here are some fixes for common problems.

Reset Your Breaker 

Locate the breaker box to check if the problem begins caused by the circuit breaker. Next, open the front panel to see the switches. They will look different depending on the model but look for a switch that needs to be fully on. Some models will have a trip setting making it easy to spot. 

To fix the issue, move the switch to the off position. Then, move the switch to the on position to ensure it is all the way on. If your panel has an indicator, it will turn off once the unit has been restored to the one position. If the power still needs to be restored, try the reset once more. If the issue still needs to be resolved, move to the next step to find the problem.

Resetting the Breaker

Reconnect Your Wires 

If you have removed the front panel and found the wires disconnected or loose, they will need to be reconnected. 

First, use the breaker to ensure the power is off and remove the batteries. Next, remove the thermostat from the base. Next, locate the screw or connecter holding the wires in place. Loosen the screw and remove the wire if needed. Take this time to examine the wires. If they appear damaged, check them with a multimeter for continuity

Connecting Wires

If the wires test fine and look clean, reconnect the wires via a screw or connector. Next, place the batteries back in the device and place it back on the wall. Finally, restore power to the unit and see if the thermostat turns on. 

Check Wire Compatibility

Some devices are only compatible with certain types of wiring. In the case of the ecobee thermostat, you will need to ensure the wires will work with the device. Many thermostats require a “C-wire” or common terminal to power the device. It is typically black or blue and might be labeled with a “C.” If you do not have the wire, your thermostat will not power on without an adapter or running a new wire. In this case, a low-voltage thermometer is needed.  Luckily the ecobee does not require this “C-wire” and will include an adapter to power the device. 

Wiring Diagram
Wiring Diagram

Many Wi-Fi and smart devices will need this wire to run; make sure you check the compatibility before removing the old thermometer and buying a new one. 

Replace Your Battery 

The most simple fix for a thermostat with no power is replacing the batteries. You can do this by removing the panel or device from the wall and exposing the inside and the batteries. Make a note of the type of batteries your thermostat uses, AA, AAA, or CR2032. Remove the old battery and replace it with a new one. It is best not to resuse old batteries for this purpose as they may need to be replaced faster or damage the device. 

Replacing the battery

Once the batteries are securely in place, return the device to the wall and ensure it snaps into place. Next, test the thermostat by turning it on and adjusting the temperature. 

Check Your Safety Switch 

If the safety switch on your HVAC unit is causing a lack of power, it will need to be checked and reset. First, locate the switch by following the steps listed above. Once it has been located, remove it from the unit. If you find an overflow of water, this is causing the switch to trigger, and it will need to be drained with the help of a wet vac. If there is no overflow, test the safety switch to ensure it works properly and does not need to be replaced. 

If it needs replacement, remove the old and install the new switch in the same way. 

What Happens If The Thermostat Loses Power?

When a thermostat loses power, it will no longer control the temperature of your home. This does not mean your HVAC will not work, but it will use more energy as there is nothing controlling the temperature. 

Also, if the thermostat loses power, the time may need a reset. This is typically only the case with non-smart thermometers, as they do not receive any information from the internet. 

Additionally, your thermostat may not have saved any settings, and they will need to be reset once power has been restored.

When To Call a Professional?

The best time to call a professional is when you feel the job is too much to handle. This typically happens when you have completed all the basic troubleshooting tasks mentioned above and still have no power to the thermometer. 

Also, if you do not feel comfortable around the wiring or you see a warning behind the thermostat regarding possible electric shock, it is best to leave it to the pros. Most wiring jobs should be handled by a professional electrician or HVAC company. 

In addition to the personal risks, improperly fixing a thermometer can lead to damaging the unit beyond repair, damaging the wiring, continually blowing fuses, and tripping circuits due to incorrect installation and damage to the HVAC unit. 

The cost of hiring a professional will depend on your location. However, the average cost is typically $125 per hour for labor and $100 to $200 for a replacement if needed. This may seem like a lot but it can be worth the money saved on wasting energy from an incorrectly installed thermometer can offset this. Also, your safety is worth more than a few dollars to have a professional do the work. 

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