How to Fix Honeywell Thermostat Cool On Blinking After Power Outage?

Experience the frustration of a malfunctioning thermostat after a power loss is an all too common scenario for homeowners. Among the issues that can arise, the Honeywell thermostat cool on blinking after power outage stands out as a perplexing concern. 

This blinking indicator, which typically signifies cooling, can leave you wondering how to restore your thermostat to its proper functionality. 

In this comprehensive guide, we will delve into the root causes of this issue and provide you with a step-by-step roadmap to successfully address and resolve the Honeywell thermostat cool-on blinking issue after a power loss. Let’s embark on this journey to troubleshoot and rectify the blinking cool-on light, ensuring your Honeywell thermostat operates seamlessly once again.

What Is ‘Cool On’ Blinking On Honeywell Thermostat?

A “cool on blinking” indicator on a Honeywell thermostat is a visual signal that there is a problem with the cooling system. When you see the “Cool On Blinking” indicator, it means that the thermostat has detected a problem that is preventing the cooling system (air conditioner or heat pump) from working as expected.

Blinking indicators act as a diagnostic tool to alert you that something is wrong and needs attention. It is designed to prompt you to investigate and take action to resolve the underlying problem that is causing the cooling system to malfunction or malfunction.

The specific causes of a “Cool On Blinking” indicator can vary and can include problems such as faulty wiring, incorrect thermostat settings, temperature sensor problems, air filter problems, electrical faults, frozen coils, or other technical faults within the cooling system.

When you encounter the “cool on blinking” indicator, it is important to follow the proper troubleshooting steps outlined in the thermostat’s manual or seek professional HVAC assistance to diagnose and correct the problem. Ignoring a blinking indicator can lead to inadequate cooling, energy inefficiency, increased utility bills, and potential damage to your cooling system if not addressed immediately.

What is the Blinking Issue After Power Loss?

Power outages can disrupt the delicate balance of electronic devices, including your Honeywell thermostat. The perplexing cool-on-blinking issue that emerges after a power loss is a manifestation of this disruption.

When power is restored, the thermostat undergoes a reset process, and the cool-on light starts blinking, indicating a problem. This section will provide insights into the significance of power loss, its impact on thermostat functioning, and why the cool-on-light blinks, setting the stage for our troubleshooting journey. 

By comprehending the mechanics behind this phenomenon, you’ll be better equipped to navigate the subsequent steps and restore your thermostat to its optimal state.

8 Causes Why Honeywell Thermostat Cool On Blinking After Power Loss

A blinking “Cool On” indicator on a Honeywell thermostat after a power outage could be due to various reasons. Here are some possible causes:

1. System Reset

Power outages can sometimes cause the thermostat’s settings to reset to default. This might lead to the blinking “Cool On” indicator as the thermostat is trying to regain communication with the cooling system.

2. Loss of Configuration

If the thermostat lost power during the outage, it might have lost its configuration settings. This could cause it to behave erratically or show unexpected indicators.

3. Cooling System Issues

The blinking indicator could be indicating a problem with your cooling system itself, rather than the thermostat. It’s possible that the cooling system’s components were affected by the power outage, or there might be an underlying issue that coincidentally arose around the same time.

4. Faulty Wiring

Power surges during an outage can sometimes cause issues with the wiring of the thermostat or the cooling system. This could lead to incorrect signals being sent to the thermostat and trigger unexpected behavior.

5. Software Glitch

Sometimes, electronic devices like thermostats can experience software glitches or bugs. A power outage might have disrupted the thermostat’s software, causing it to display the blinking indicator.

6. Battery Backup

Some Honeywell thermostats come with battery backup to maintain settings during power outages. If the battery is low or not functioning properly, it could lead to strange behavior once power is restored.

7. Communication Errors

After a power outage, there could be communication errors between the thermostat and the cooling system. This could be due to a variety of factors, including temporary issues with the thermostat’s communication module or the cooling system’s controller.

8. Hardware Damage

In rare cases, a power surge during an outage could have damaged the internal components of the thermostat, leading to malfunctioning behavior.

What Can Happen When Honeywell Thermostat Cool On Blinking?

When a Honeywell thermostat’s “Cool On” indicator is blinking, it typically indicates that there is an issue with the cooling system. The specific consequences and outcomes of this blinking indicator can vary based on the underlying problem. Here are some potential scenarios and outcomes that can occur when the Honeywell Thermostat Cool On is blinking:

No Cooling

The most immediate consequence is that your cooling system (air conditioner or heat pump) may not be functioning as expected. This can result in inadequate cooling or no cooling at all, causing discomfort and potentially affecting indoor air quality.

Temperature Imbalance

The blinking indicator could lead to temperature imbalances in your home. Certain areas might be cooler than desired while others remain warmer due to the system’s inability to distribute conditioned air properly.

Energy Inefficiency

A malfunctioning cooling system can lead to energy inefficiency, as the system may run longer and consume more energy than necessary to achieve the desired temperature.

Increased Energy Bills

With the cooling system working harder to maintain the set temperature, your energy bills could increase significantly if the issue is not resolved promptly.

System Wear and Tear

Continuous operation of a cooling system under faulty conditions can lead to increased wear and tear on the components. This can result in premature system failures and the need for costly repairs or replacements.

Indoor Comfort Issues

If the cooling system isn’t functioning properly, it can lead to discomfort and reduced indoor air quality, especially during hot weather. This can impact your overall well-being and the comfort of your household.

HVAC Damage

Depending on the underlying cause of the blinking indicator, there’s a possibility of damaging your HVAC (Heating, Ventilation, and Air Conditioning) system further if the issue is not addressed promptly.

Inaccurate Temperature Control

The blinking indicator might indicate a problem with the thermostat’s temperature sensing or control, leading to inaccurate temperature readings and difficulty maintaining a consistent and comfortable indoor environment.

Frozen Coils

In some cases, a blinking “Cool On” indicator could be a result of frozen evaporator coils. This can reduce the cooling capacity of the system and may even cause the compressor to shut down to prevent further damage.

Mold Growth

A malfunctioning cooling system can lead to improper humidity control, creating conditions conducive to mold growth in your home.

Troubleshooting Steps to Diagnose and Resolve the Blinking ‘Cool On’ Indicator Issue

here’s a detailed breakdown of the troubleshooting steps for addressing the Honeywell Thermostat Cool On Blinking issue:

Step 1: Verify Wiring

  1. Turn off power to the thermostat and cooling system at the circuit breaker.
  2. Gently remove the thermostat cover to access the wiring.
  3. Carefully inspect the wiring connections to ensure they are properly attached to their respective terminals.
  4. If any wires are loose or improperly connected, securely reattach them according to the thermostat’s manual or labeling.
  5. Replace the thermostat cover and restore power to the thermostat and cooling system.
  6. Check if the blinking indicator persists. If the issue remains, proceed to the next step.

Step 2: Check Settings

  1. Access the thermostat’s settings menu by navigating through the user interface as indicated in the manual.
  2. Review the cooling settings, including the set temperature and cooling mode.
  3. Adjust the settings if necessary, making sure the desired temperature is set and the cooling mode is selected.
  4. Save the changes and observe if the blinking indicator is resolved. If not, proceed to the next step.

Step 3: Temperature Differential Adjustment

  1. Refer to the thermostat’s manual to understand how to access the temperature differential setting.
  2. Adjust the temperature differential to a suitable value. The temperature differential determines when the cooling system turns on and off based on the difference between the set temperature and the actual room temperature.
  3. Save the changes and monitor if the blinking indicator persists. If the issue continues, proceed to the next step.

Step 4: Inspect Air Filter

  1. Turn off power to the cooling system at the circuit breaker.
  2. Locate the air filter in the air handler or furnace unit.
  3. Remove the air filter and visually inspect it for dirt, dust, and debris.
  4. If the filter is dirty or clogged, replace it with a new one of the appropriate size and type.
  5. Turn the cooling system’s power back on and observe if the blinking indicator is resolved. If not, proceed to the final step.

Step 5: Power Cycling

  1. Turn off power to the thermostat and cooling system at the circuit breaker.
  2. Wait for a few minutes to ensure any residual power is discharged.
  3. Turn the power back on to the thermostat and cooling system.
  4. Allow the system to go through its startup sequence and check if the blinking indicator is no longer present.

Advanced Fixes for Honeywell Thermostat Cool On Blinking Issue

While the initial troubleshooting steps can often resolve the Honeywell thermostat cool on blinking issue, there are instances where more advanced measures may be necessary. 

Voltage Issues

In some cases, the blinking cool on light could be a result of an incorrect voltage supply. Fluctuations in voltage can disrupt the thermostat’s operation. If you suspect voltage irregularities, it’s advisable to seek professional assistance. 

An HVAC technician can assess the voltage supply and address any underlying electrical problems to ensure consistent and stable power delivery to the thermostat.

Software Updates

Outdated firmware or software can sometimes lead to unexpected issues with thermostat operation. Check Honeywell’s official website for any available software updates for your thermostat model. 

Updating the software can often resolve compatibility issues and improve overall performance. If you’re unsure about the update process, consider reaching out to Honeywell’s customer support for guidance.

Sensor Calibration

Accurate temperature readings are crucial for proper thermostat function. If your thermostat’s temperature sensors are not calibrated correctly, it can lead to erratic behavior, including the cool on blinking issue. 

Refer to your thermostat’s user manual to understand how to calibrate the temperature sensors accurately. Follow the provided instructions to recalibrate the sensors and ensure precise temperature measurements.

If you’ve followed all these troubleshooting steps and the “Cool On Blinking” issue exists, it’s recommended to contact professional HVAC technicians or Honeywell customer support for further assistance. They can diagnose more complex issues and provide appropriate solutions to ensure your cooling system operates as intended.

3 Preventive Measures for Cool-On Blinking Issues After Power Loss

Addressing the Honeywell thermostat cool-on blinking issue after a power loss is essential, but it’s equally important to take proactive steps to prevent such occurrences in the future. 

1. Surge Protectors for HVAC Systems

Power surges are a common cause of electronic malfunctions after power outages. Installing surge protectors specifically designed for HVAC systems can safeguard your thermostat and other sensitive equipment from voltage spikes. 

These devices act as a barrier, absorbing excess voltage and preventing it from reaching your thermostat. Investing in surge protectors is a smart strategy to shield your HVAC system from potential damage during power fluctuations.

2. Regular Maintenance and Inspections

Just as your car needs regular maintenance to function optimally, your thermostat and HVAC system benefit from periodic inspections. Schedule routine maintenance checks with a professional technician to ensure all components are in good working condition. 

During these inspections, potential issues can be identified and addressed before they escalate into major problems. Maintenance can also involve cleaning, lubrication, and calibration of critical parts, contributing to the longevity and reliability of your thermostat.

3. Battery Backup Systems

Integrating a battery backup system with your Honeywell thermostat adds an extra layer of protection against power outages. During electricity disruptions, the battery backup kicks in, allowing your thermostat to maintain essential settings and configurations. 

While the power outage may still occur, your thermostat will continue functioning seamlessly, preventing the cool-on-blinking issue and minimizing disruptions to your comfort.

Frequently Asked Questions (FAQ’s)

Why is my Honeywell thermostat’s cool on light blinking after a power loss?

The blinking cool on light indicates a disruption in the thermostat’s operation caused by a power loss. It’s a sign that the thermostat needs attention and may require troubleshooting to restore proper functionality.

Can I fix the cool on blinking issue on my Honeywell thermostat myself?

Yes, many cool on-blinking issues can be resolved through simple troubleshooting steps. This guide provides a comprehensive set of instructions to help you diagnose and fix the problem. However, if you’re uncomfortable with technical tasks, seeking professional assistance is advisable.

Why is sensor calibration important in addressing the cool-on-blinking issue?

Sensor calibration ensures accurate temperature readings, which are crucial for proper thermostat operation. Incorrect sensor readings can lead to erratic behavior, including the cool on the blinking issue. Recalibrating the sensors helps maintain precise temperature control.

What are surge protectors, and how do they help prevent thermostat issues after power outages?

Surge protectors are devices designed to safeguard electronic equipment from voltage spikes caused by power surges. Installing surge protectors for your HVAC system, including the thermostat, helps prevent damage and malfunctions during power fluctuations, reducing the chances of encountering issues like the cool-on-blinking problem.


In the realm of home comfort, the Honeywell thermostat serves as a vital control center for your HVAC system. The perplexing cool-on-blinking issue that emerges after a power loss can disrupt this harmony, leaving you searching for solutions. 

By embarking on this troubleshooting journey and understanding the dynamics behind the issue, you’ve taken a significant step toward restoring your thermostat’s optimal functionality.

In the end, your commitment to resolving the Honeywell thermostat cool on blinking issue reflects your dedication to maintaining a comfortable and functional living environment. As you apply the insights gained from this guide, you’re not only restoring your thermostat’s performance but also enhancing your overall understanding of HVAC systems.

Scott Maupin