9 Reasons Your Honeywell Thermostat Not Turning On

A thermostat is something on which we highly rely on it to keep the surrounding atmosphere comfortable. But it is annoying to see it not turning on when you are in dire need of it. What could be the possible reasons?

The primary reasons are low batteries, power supply issues, wiring issues, dirty or faulty sensors, outdated firmware, or network issues. You can rule out the problems one by one. Resetting solves most issues simultaneously, but it should be the last resort. 

This article shares all the possible causes behind a Honeywell thermostat not working and how to troubleshoot these causes and start the thermostat all over. If you have faced any of these issues, and are searching for solutions, stick to this article till the end.

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1. Power supply issues 

If the thermostat is not receiving enough power, it won’t start to work. 

Power supply issues could include a power outage, tripped circuit breaker, or a switch not turned on. 

Someone must have accidentally turned off the switch, and you are unaware of it. 

As a result, when you try starting the thermostat, it won’t start. 

Check the power switch of the thermostat and your house’s HVAC systems. 

If there is still no power, check for tripped breakers. Breakers can trip due to overloading or power surges. 

Go to the thermostat and the HVAC breakers and see whether they have tripped. 

The switch will either be in the off position or stuck in the center. 

If the switch is in the off position, flip it on and hold it until you hear the clicking sound. 

Your system and the device should start after 10 to 15 minutes. 

If the switch is stuck at the center, turn it off, wait a few seconds, turn it on, and hold it until the click sound. 

If there is a RESET button, press it for a few seconds until you hear a clicking sound.

Remember that if the breaker trips immediately after the resetting, you should leave it like that and call a professional for help. 

If the thermostat still does not work, check for a power outage. In that case, you have to wait for the power to return. 

Also read: 11 Reasons Why Your Honeywell Thermostat Is Blank

2. Battery issues 

The Honeywell thermostat works with two AA or AAA alkaline batteries.

Your device will not turn on when the batteries are low, or connections are faulty. 

Over time, some bad conditions develop between the batteries and the battery holder’s terminals. 

In such conditions, a close inspection can identify the problem. 

Open the battery compartment and examine it closely. 

Old batteries become dirty and rusted, creating a poor connection in the holder. 

Check the thermostat’s display if you cannot understand anything from the inspection. 

It will show NO POWER SOURCE when the batteries are dead, or their connections are faulty. 

So, replace them with two new AA/AAA batteries. 

To prevent this problem, replace the batteries every 10 to 12 months. 

To replace the batteries:

  1. Turn off the thermostat and the breaker. 
  2. Most Honeywell thermostats can slide out of the wall mounting. 
  3. Remove the device from the wall and open the battery compartment. 
  4. Remove the old batteries, and clean the battery holder terminals. 
  5. Do not take too much time. Otherwise, the thermostat will factory reset, and you will have to reprogram it anew. 
  6. Insert the two new AA/AAA batteries and close the compartment. Mount back the thermostat. 
  7. Please switch it on and check its functionality. 

3. Thermostat settings 

Here, the problem occurs when you consider a DIY for your thermostat.

When you try upgrading the HVAC or the thermostat, you may have the wrong configuration or setting. 

As a result, programming errors won’t let your thermostat turn on. 

To fix the problem, you need to consult the manual to fix the thermostat setting. 

Consult the owner’s manual for proper details and correct configuration.

You can also follow the following basic steps that I follow for a correct thermostat configuration:

  1. Ensure you have the thermostat’s DATE CODE. If you don’t have one, locate it on the thermostat’s back and write it down.
  2. Tap the MENU option and select INSTALLER.
  3. When the screen prompts DATE CODE, enter it, and your installation settings will be shown on the screen. 
  4. The manual will explain everything you want to know about programming the thermostat. 
  5. If you still can’t figure it out, hire a professional.

4. Wiring issues 

Wrong, damaged, and loose wiring will prevent your Honeywell thermostat from turning on. But don’t worry. 

Like the previous issue, you can fix this with a few DIY videos, research, and your manual. 

When the wires are damaged or loose, the thermostat fails to detect the surrounding temperature or receives enough power. 

So, it will either malfunction or won’t start. 

Turn off the circuit breaker and remove the cover plate of the device to examine the wires.

Make sure the wires are connected to their respective terminals. 

The terminals will be labeled with the same alphabets as the wires, for example, R-wire to the R terminal, W-wire to the W terminal, C-wire to the C terminal, etc.

Especially check the C-wire. 

The Common wire powers the smart thermostat constantly to operate it day and night. 

Check whether the wires are appropriately secured. 

If they feel tight, tighten them a bit.

Put your thermostat back into the wall, turn on the breaker, and start the thermostat. 

Please wait for some time to see whether it works.

But if the problem persists, call a professional for help. 

5. Firmware updates

If you have a digital thermostat, firmware updates are essential. 

Without this update, your thermostat won’t work correctly and, over time, stop turning on.

So, you need to check for the updates regularly and update them for proper functionality. 

To check and update the firmware of your Honeywell thermostat:

  1. Open the thermostat application on your mobile phone.
  2. Go to the FIRMWARE tab and click on SCAN FOR UPDATES. 
  3. Wait for some seconds to see if there is an update. 
  4. If there is, it will pop up on the screen. 
  5. Click on the DOWNLOAD and install the recent update.
  6. Try turning on your thermostat after that. 

6. Network issues 

If you have an intelligent Honeywell thermostat, it will need an internet connection to function. 

Without proper Internet or Wi-Fi signals, the thermostat will not turn on. 

So, you won’t be able to enjoy all the device’s features.

There are several network-related issues:

  • No internet connection
  • No many interferences
  • Wrong Wi-Fi band

To ensure your thermostat turns on:

  1. Check if you have an internet connection. If there isn’t any, try resetting the router or the thermostat. 
  2. The thermostat will not receive enough network signals if you have connected too many devices to the same router. So, reduce the traffic. 
  3. Also, make sure that the thermostat is within the internet range. Reduce physical obstructions too. 
  4. When using Wi-Fi, connect the thermostat to the 2.4 GHz band. The thermostats are incompatible with the 5 GHz. Band. 

7. Airflow blockage 

Air filters allow enough airflow to pass through your house’s heating and cooling systems. 

If the airflow gets blocked due to dirty or clogged filters, it will affect the efficiency of the HVAC system. 

Another reason for airflow blockage is closed vents. With closed vents, airflow is inefficient. 

If the airflow is insufficient, the thermostat will stop turning on over time.

To fix the problem, regularly replace the air filters every 3-4 months and open the closed vents of your HVAC system. 

Remove obstacles around the thermostat and the outdoor HVAC units for adequate airflow.

8. Dirty sensor or thermostat 

The sensor in the thermostat senses the surrounding temperature. 

Then the device can provide a reading of the room temperature. 

The sensor is the main thing in the thermostat. 

Without this, the device cannot function properly. 

The thermostat will not detect the temperature or turn on if it is dirty or faulty. 

To fix the problem, open your thermostat and clean it, especially around the sensor. 

If the sensor is damaged, you must call a professional to replace it. 

9. Access door 

Every minor thing in the Honeywell thermostat will matter, the access door being one of them. 

Open access doors will not let your thermostat turn on out of safety. 

There are safety measures in the Honeywell thermostats, like the HVAC systems. 

I faced it once. After much checking, I discovered that open access doors keep your thermostat from turning on due to safety.

So, when the access door of the HVAC remains slightly open, the thermostat’s inner safety features won’t let it function. 

To fix the problem, check which access doors you have left open. Close, lock, and secure them properly. 

Start the thermostat again to see if it is working. 

Every time you start the thermostat, ensure you have closed all the access doors. 

When should I reset my Honeywell thermostat?

The above-discussed problems are some common reasons behind a thermostat not turning on. 

I have faced a few of them and solved them with some research and DIY videos. 

Resetting the thermostat can work if you cannot fix the problems with the mentioned troubleshooting steps. 

So, consider this as your last resort. 

Remember that factory resetting the Honeywell thermostat will delete all the previously set features. 

After your thermostat comes back, you have to set them up again. 

A general resetting method for the Honeywell thermostat involves the following steps:

  1. Go to the touch screen and select the MENU or HOME SCREEN. 
  2. Press the SIDE arrow until you see the RESET button. 
  3. Select the option and click on FACTORY RESET. 
  4. Confirm and wait for some time for the device to come back. 

However, the resetting steps can differ based on your Honeywell thermostat type. 

An owner manual will be the best guide for resetting your Honeywell thermostat. 

However, I am still adding some resetting steps in brief for some specific Honeywell models:

Honeywell 4000 series

  1. Keep the device on.
  2. Locate the button named PROGRAM. 
  3. Press and hold the button for a few seconds. 
  4. Release it, and your thermostat should factory reset.

Honeywell 6000 series

  1. Keep the device on. 
  2. Hold the FAN button and the UP arrow together. 
  3. Keep holding until you see 39 popping on the display screen. 
  4. Press the DOWN arrow keys until the number changes to 0.
  5. Now, press the DONE key again, and reset the thermostat. 

Honeywell 7000 series 

  1. Please turn off the thermostat and remove it from the wall plate. 
  2. You will see two separate batteries. 
  3. Remove and insert them in the opposite direction.
  4. After 5 seconds, remove them again and insert them in the correct position. 
  5. It will reset the thermostat, and the display will turn on. 
  6. Restore the power to the device for a complete reset.

Honeywell 8000 series 

  1. Keep the device on, and press the SYSTEM button over the screen. 
  2. Hold it for 5 seconds.
  3. An option will pop up saying RESET TO FACTORY SETTINGS. 
  4. Select the option and reset your thermostat. 

Final thoughts

There are numerous reasons behind a thermostat not turning on. I have pointed out some common issues I am aware of. Many potential problems mentioned in the article have simple fixes; you can solve them yourself with research. 

Besides, remember the manual, as it will solve most of the issues you face. For smart thermostats, especially pay attention to the C-wire as it powers the Wi-Fi thermostats constantly to operate throughout the day and night.

But if the problem remains, reset your thermostat as a last resort. If you still cannot fix the problems, your thermostat might have serious issues that need an expert’s attention. 

How will the thermostat know when you turn on the heat or cool air?

Usually, you control the thermostat to set a desired temperature. But digital thermostats learn your preferences. Besides, some have an AUTO-ADJUSTED mode that turns the thermostat from HEAT to COOL by detecting the surrounding temperature.

Why doesn’t Honeywell’s thermostat turn on the heat?

Possible reasons include faulty wiring, wrong location, weak batteries, furnace turned off, tripped breaker, broken thermostat, or wrong configuration. Check the problems individually to troubleshoot them.

Reference: Thermostat Wikipedia

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Arthur Smith

Howdy! I am Arthur Smith, an electrical engineer who is extremely passionate about electronics. I have lived in different parts of the US and currently reside in Wisconsin. I am one of those rare children who knew what he wanted to study and do in life right from the start. I was a curious child who wanted to know how switches work and how the AC works, and I would always observe my dad whenever he would handle the wires and fix things around the house. I currently work as an electrical engineer at a reputed company and write for this blog. And I read loads of books or play video games in my free time.

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