Honeywell Thermostat Says AC Power Loss: Here What To Do!

AC says power loss on your Honeywell thermostat can be a frustrating and concerning issue, especially when your HVAC system is not functioning as expected. 

When your Honeywell thermostat says ac power loss message, it’s essential to address it promptly to maintain a comfortable indoor environment and prevent potential damage to your heating and cooling system.

In this comprehensive guide, we will explore the common causes of AC power loss Honeywell thermostats, offer step-by-step troubleshooting instructions, and provide valuable tips on preventative maintenance. 

Let’s delve into the world of troubleshooting Honeywell thermostat ac power loss.

Table of Contents

what does aC power loss mean on honeywell thermostat?

Before we dive into troubleshooting, it’s crucial to grasp what does ac power loss mean on honeywell thermostat

AC power loss occurs when the thermostat loses its connection to the electrical power source that keeps it running. 

This disruption can result from various factors, and understanding them is the first step in resolving the issue effectively. Here are some key points to define this:

Thermostat Dependency

Honeywell thermostats rely on electrical power to function correctly. They use this power to display temperature information, control your HVAC system, and communicate with other devices.

Backup Batteries

Some Honeywell thermostat models come equipped with backup batteries. These batteries can temporarily power the thermostat during a power outage, preventing immediate loss of control over your HVAC system.

However, they are limited in capacity and duration.

Importance of Power

When AC power is lost, your thermostat may become unresponsive, and you might not be able to adjust temperature settings. This can lead to discomfort and energy inefficiency.

Indicator Message

Your Honeywell thermostat may display a message like “AC power loss” or “No power” to alert you to the issue.

Potential Causes

AC power loss can be caused by a range of factors, including electrical problems, issues with thermostat wiring, or problems with your HVAC system itself.

8 Common Causes of Honeywell Thermostat Says AC Power Loss

When your Honeywell thermostat displays an “AC power loss” message, it’s essential to identify the underlying cause so you can take appropriate action. 

AC power loss can occur due to a variety of reasons, and understanding these common causes will help you troubleshoot effectively. Here are some of the typical culprits:

1. Electrical Outages

The most obvious cause of AC power loss is a power outage in your area. When your home loses electrical power, your thermostat will also lose power.

2. Tripped Circuit Breaker

Check your home’s circuit breaker panel. If the circuit supplying power to your thermostat has tripped, it will cut off power to the thermostat.

3. Loose Wiring

Loose or disconnected wiring in your thermostat can disrupt the electrical connection. Inspect the thermostat’s wiring to ensure all connections are secure.

4. Dead Batteries

If your thermostat has backup batteries, they may be depleted or dead. These batteries are crucial during power outages, so they need to be regularly checked and replaced.

5. HVAC System Issues

Problems with your heating or cooling system can also trigger AC power loss. Faulty HVAC components or a malfunctioning control board may cause power interruptions to the thermostat.

6. Thermostat Settings

In some cases, incorrect thermostat settings or programming errors can make it appear as though there’s an AC power loss. Review your thermostat settings to ensure they are configured correctly.

7. Faulty Transformer

The transformer that converts electrical power for your thermostat may be faulty. This component can degrade over time and cause intermittent power issues.

8. Wiring Short Circuits

Short circuits in the thermostat’s wiring can disrupt the power supply. Inspect the wiring for any signs of damage or wear.

How to Fix AC Power Loss On Your Honeywell Thermostat? – Step By Step

Now that you’re familiar with the common causes of AC power loss honeywell thermostat, let’s walk through a series of troubleshooting steps to help you identify and resolve the issue. 

Follow these steps in sequence to systematically diagnose and fix the problem:

Step 1: Check the Thermostat Display

– Begin by inspecting the thermostat display. Look for any error messages such as AC power loss or No power. Note down the exact message displayed.

Step 2: Verify Power Sources

– Ensure that your thermostat is securely connected to its power source. This typically involves checking the wiring and ensuring it’s properly connected to the HVAC system and the power source.

Step 3: Inspect Circuit Breakers

– Examine your home’s electrical circuit breaker panel. Locate the circuit breaker that supplies power to your thermostat and HVAC system. 

If it’s tripped, reset it by switching it off and then back on.

Step 4: Test the HVAC System

– Check whether your heating or cooling system is operating correctly. If the HVAC system itself is experiencing issues, it could lead to AC power loss on your thermostat.

Listen for unusual noises or observe any error codes on the HVAC unit.

Step 5: Replace Backup Batteries

– If your Honeywell thermostat has backup batteries, replace them with fresh ones. Weak or depleted batteries can trigger AC power loss messages. 

Refer to your thermostat’s manual for specific battery replacement instructions.

Step 6: Inspect Wiring

– Carefully inspect the thermostat’s wiring for any loose, disconnected, or damaged connections. If you find any issues, gently reconnect or repair the wiring as needed.

Step 7: Reset the Thermostat

– If none of the above steps resolves the issue, try resetting your thermostat. Refer to your thermostat’s manual for instructions on performing a factory reset. 

Keep in mind that this step may erase your previous settings, so make note of them before resetting.

Step 8: Seek Professional Help

– If you’ve gone through these troubleshooting steps and still experience AC power loss on your Honeywell thermostat, it may be time to consult a professional HVAC technician. 

They can diagnose and address more complex issues with your HVAC system or thermostat.

Reset Honeywell Thermostat

If you’ve tried the previous troubleshooting steps and are still experiencing AC power loss on your Honeywell thermostat, resetting the thermostat may solve your problem. 

Resetting the thermostat can often resolve software or configuration issues that might be causing the problem. Here’s how to reset your Honeywell thermostat:

Locate the Reset Button

– Depending on your Honeywell thermostat model, the reset button may be located on the front, side, or back of the device. Refer to your thermostat’s user manual for the exact location of the reset button.

Power Off the Thermostat

– Turn off the power supply to your thermostat. This typically involves switching off the circuit breaker that controls the thermostat or disconnecting it from the wall if it’s battery-powered.

Press and Hold the Reset Button

– Using a small tool or a paperclip, press and hold the reset button for approximately 5 to 10 seconds. The thermostat’s display may flash or go blank during this time.

Restore Power

– After holding the reset button, restore power to the thermostat by either turning the circuit breaker back on or reconnecting the device to the wall, depending on your setup.

Reconfigure Your Thermostat

– Once the thermostat reboots, it will be reset to its default factory settings. You’ll need to reconfigure it with your desired settings, such as temperature preferences, programming schedules, and Wi-Fi connectivity.

Test for AC Power Loss

– Monitor your thermostat to see if the AC power loss issue has been resolved. If the message no longer appears, and your thermostat functions correctly, you’ve successfully reset it.

Preventative Maintenance for Honeywell Thermostat AC Power Loss

Preventative maintenance is the key to avoiding AC power loss issues and ensuring your Honeywell thermostat operates reliably. 

By taking proactive steps to care for your thermostat and HVAC system, you can minimize the risk of disruptions and maintain a comfortable indoor environment. Here are some essential preventative maintenance tips:

Regular Thermostat Maintenance

  • Dust and Clean

Periodically clean the thermostat’s display and surrounding area to prevent dust buildup, which can affect visibility and performance.

  • Battery Checks

If your thermostat uses backup batteries, replace them at least once a year or as recommended in the user manual.

  • Software Updates

Check for firmware updates for your thermostat model and apply them if available. Updated software can improve performance and address known issues.

Proper Wiring and Connections

   – Ensure that all wiring connections are secure and not damaged. Loose or frayed wires can lead to power loss or erratic behavior.

   – Label and document the wiring connections when installing or replacing the thermostat. This will make troubleshooting easier in the future.

HVAC System Maintenance

  • Regular HVAC Servicing

Schedule annual or bi-annual maintenance for your heating and cooling system with a qualified technician. They can inspect and tune up your HVAC system, reducing the risk of issues that could affect your thermostat.

  • Air Filter Changes

Replace air filters in your HVAC system according to the manufacturer’s recommendations. Clogged filters can strain the system and lead to problems.

  • Clean Vents and Ducts

Ensure that vents and ducts are clean and free from blockages. Obstructed airflow can affect the performance of your HVAC system and thermostat.

Surge Protection:

   – Consider installing surge protectors for your thermostat and HVAC equipment. Power surges can damage sensitive electronics, including your thermostat.

Temperature Settings

   – Set temperature schedules that align with your household’s daily routines. Avoid frequent adjustments, as rapid temperature changes can strain the HVAC system.

Environment Control

   – Keep your thermostat away from direct sunlight, drafts, or sources of heat. Extreme temperature fluctuations can affect its accuracy.

Wi-Fi Connectivity

   – If your thermostat connects to Wi-Fi, periodically check its connection status. Weak or lost Wi-Fi signals can disrupt communication between your thermostat and your smartphone or other devices.

Honeywell Thermostat AC Power Loss Alert

Honeywell thermostats often come equipped with features that can alert you to power loss or other issues. Here’s how you can set up an AC power loss alert on a Honeywell thermostat:

Access the Menu

Depending on your specific Honeywell thermostat model, you may need to access the menu. Usually, this involves pressing the “Menu” button or touching the screen.

Select Settings

Navigate through the menu options until you find the “Settings” or “System Settings” option.

Power Loss Alert

Look for a sub-menu related to alerts or notifications. You may find an option for “Power Loss Alert” or something similar.

Enable the Alert

Once you’ve located the power loss alert option, enable it. This usually involves selecting “On” or a similar option.

Adjust the Settings

You might have the option to set a specific threshold for the alert, such as how long the power needs to be out before it triggers. Adjust these settings according to your preferences.

Save and Exit

After configuring the alert settings, make sure to save your changes and exit the menu.

Remember that the exact steps and wording of the menu options can vary depending on your Honeywell thermostat model. Refer to your thermostat’s user manual for precise instructions tailored to your device.

Additionally, keep in mind that power loss alerts might require your thermostat to have a backup power source, such as batteries, to function properly during power outages. Ensure that your thermostat is correctly set up and powered to receive these alerts.

When to Seek Professional Help on AC power loss Honeywell thermostat Issue?

While many AC power loss Honeywell thermostat issues can be resolved through DIY troubleshooting, there are situations where it’s advisable to seek the expertise of a professional HVAC technician. 

Here are some signs that indicate it’s time to call in a professional:

Persistent AC Power Loss

If the AC power loss issue continues despite your best efforts to troubleshoot and reset the thermostat, it may be a sign of a deeper, underlying problem that requires professional diagnosis.

HVAC System Malfunctions

If your HVAC system is experiencing issues beyond what the thermostat displays, such as strange noises, inconsistent heating or cooling, or frequent system failures, it’s essential to involve an HVAC technician. 

These problems may be interconnected with the thermostat issue.

Electrical Problems

If you suspect that the power loss issue originates from electrical problems within your home’s wiring or circuitry.

It’s safer to have an electrician inspect and address these issues. Faulty wiring can pose a significant safety risk.

Complex Wiring Issues

If you’ve identified complex wiring problems during your troubleshooting process, or if you’re uncomfortable working with electrical components.

It’s wise to enlist the help of a professional technician who specializes in thermostat and HVAC system installations and repairs.

Out-of-Warranty Equipment

If your thermostat is still under warranty, professional assistance may be necessary to avoid voiding the warranty. 

Attempting extensive DIY repairs on a covered device could result in warranty issues.

Safety Concerns

If you encounter any unusual smells, smoke, or sparks when working with your thermostat or HVAC system, prioritize safety. 

Immediately turn off the power and contact a professional technician.

Lack of Experience

If you’re unsure about any aspect of diagnosing or fixing the problem, it’s better to err on the side of caution and consult a professional. 

They have the knowledge and tools to safely and accurately resolve complex issues.

System Replacement or Upgrade

If your thermostat or HVAC system is outdated or inefficient, you might consider a replacement or upgrade. 

Professional technicians can recommend and install modern, energy-efficient solutions tailored to your needs.

Frequently Asked Questions (FAQs)

What should I do if the thermostat reset doesn’t resolve the AC power loss issue?

If resetting the thermostat doesn’t solve the problem, you should seek professional help from an HVAC technician. There may be underlying issues with your thermostat or HVAC system that require expert diagnosis and repair.

Is it safe to troubleshoot my thermostat’s electrical components myself?

Basic troubleshooting like checking connections can be done safely by homeowners. However, if you encounter complex electrical issues or feel uncomfortable working with wiring, it’s best to consult a professional to ensure safety.

How often should I replace the backup batteries in my thermostat?

It’s a good practice to replace backup batteries in your thermostat at least once a year or as recommended in the user manual to ensure they are fresh and functional during power outages.

Can a power surge damage my thermostat?

Yes, power surges can potentially damage sensitive electronic components in your thermostat. Consider installing surge protectors for your thermostat and HVAC equipment to mitigate this risk.

What should I do if I smell burning or notice sparks when troubleshooting my thermostat?

Safety should be your priority. Immediately turn off the power and avoid further handling of the thermostat. Contact a professional technician to inspect and address the issue.

Can a low battery cause the ‘AC Power Loss’ message?

Yes, a low battery can trigger this message, especially in battery-powered Honeywell thermostats. If your thermostat uses batteries, replace them with fresh ones to see if it resolves the issue.

Can a power surge cause this message to appear?

Yes, power surges can disrupt the power supply to your thermostat, leading to an ‘AC Power Loss’ message. Consider using surge protectors to safeguard your thermostat and HVAC system against such electrical fluctuations.


By understanding the causes of AC power loss on thermostat, mastering troubleshooting steps, and implementing preventative maintenance practices, you can keep your thermostat and HVAC system running smoothly. 

Regular care and attention to your thermostat not only ensure consistent comfort but also contribute to energy efficiency and cost savings.

Remember that safety is paramount when dealing with electrical components, and if you ever feel uncertain or encounter complex issues, don’t hesitate to consult a professional HVAC technician. 

Now equipped with the knowledge and guidance provided in this guide, you can confidently address AC power loss Honeywell thermostat, ensuring a more comfortable and stress-free living environment for you and your family.

Scott Maupin