Honeywell Pro Series Thermostat Troubleshooting

Here is a compilation of a few of the most problems questions by lyric Honeywell home pro series thermostat users and a complete guide on how to troubleshoot them in detail.

So here are Honeywell Pro Series Thermostat Troubleshooting

Honeywell Thermostat Troubleshooting No Display

  • Check the circuit breaker and reset it if necessary.
  • Make sure the power switch for the heating & cooling system is on.
  • Make sure the furnace door is closed securely.
  • Make sure fresh AA alkaline batteries are correctly installed

How to Installed Batteries?

  • Batteries are optional (to provide backup power) if your thermostat was wired to run on AC power when installed. If your thermostat Honeywell was not wired to run on AC power, then batteries are required.
  • Install fresh batteries immediately when the low battery icon appears. The icon appears about two months before the batteries are depleted.
  • Even if the low battery icon does not appear, you should replace batteries once a year, or before leaving home for more than a month.
  • If batteries are inserted within two minutes, the time and day will not have to be reset. All other settings are permanently stored in memory and do not require battery power.
  • NOTE: When replacing batteries, alkaline batteries are recommended.
  • Learn More about each series with model Honeywell battery replacement:

Heating or cooling system does not respond

  • Press Mode button to set system Heat (see below)

Make sure the desired temperature is set higher than the inside temperature.

  • Press Mode button to set system Cool (see below)

Make sure the desired temperature is set lower than the inside temperature.

  • Check the circuit breaker and reset if necessary.
  • Make sure the power switch for the heating & cooling system is on.           
  • Make sure the furnace door is closed securely.
  • Wait 5 minutes for the system to respond.

How to Press the Mode button To set the System?

  1. Press the Mode button on a programmable touchscreen to cycle to the next available System mode.
  2. Cycle through the modes until the required System mode is displayed and leave it to activate.

NOTE: Available System modes vary by model and system settings.

System modes: ‒ Auto‒ Heat‒ Cool‒ Off‒ Em. Heat

Honeywell T4, T6 Pro no programmable touchscreen option

  • From the home screen, press the MENU button.
  • Then press “+” until “prog” is displayed on the screen.
  • Then press SELECT to edit the program.

If you don’t see the program option when following these steps, the thermostat operation may have been configured as non-programmable by the installer.

Then Check ISU Settings

  1. Press and hold the CENTER and + buttons for approximately 3 seconds to enter the advanced menu.
  2. Press Select to enter ISU.
  3. Press Select to cycle through menu setup options.
  4. Press + or – to change values or select from available options.
  5. Press Select and confirm your settings or press Back to ignore changes and return to the ISU menu screen to continue editing another setup option.
  6. To finish the setup process and save your setting, press Home and return to Home screen.

Temperature settings do not change

  • If the display says “unlock“.  
  • Press the Mode button to cycle to the next available System mode.
  • Cycle through the modes until the required System mode is displayed and leave it to activate.
  • If not, verify you are in the correct mode (heat, cool, em heat, or auto); (see up of how to Press the mode button to set the system)
  • If the temperature sensor is in the correct mode, but you cannot set the heat from 40 °F to 90 °F (4.5 °C to 32 °C), or set the cool from50 °F to 99 °F (10 °C to 37 °C), you may have range-stops restricting your setting.

“Cool On” or “Heat On” is flashing

The compressor protection feature is engaged. Wait 5 minutes for the system to restart safely, without damage to the compressor

Honeywell Pro series Thermostat Reset

  1. Press and hold the menu button until the advanced menu opens.
  2. Go to “Advanced Reset” using left and right arrows.
  3. Press on “Factory”
  4. Press on the tick icon to confirm the rest.

2nd Method of Honeywell Pro series Thermostat Reset (T4, T6)

  1. Press the Menu and + button simultaneously. 
  2. Hold for 3 to 5 Seconds.

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        3. Until you see ISU pop-up display.

        4. Next press the Select and then Home button.

Honeywell Pro Series Thermostat Troubleshooting
Honeywell Pro Series Thermostat Troubleshooting


In case you have other Honeywell pro series thermostat to reset then then there is a sub topic where you can find all series thermostat reset guide. 

How to unlock/lock Honeywell Pro thermostat

The thermostat Honeywell has 3 settings for the screen lock: Unlocked, Partial Lock, and Full Lock

-Unlocked: All settings are adjustable

-Partial: Setpoint changes are allowed. All other settings are locked

-Full: No changes are allowed

When SCREEN LOCK is active, a “lock” icon will be displayed on the thermostat display

  1. Press Menu on the thermostat.
  2. Press + or to go to LOCK. Press Select.
  3. Press + or to go to OFF, PART, or ON, and then press Select.
  4. To unlock the keypad, press the CENTER button and then enter the password “1234”. To enter the password, press + or to change the first digit of the number. Then press Select. Repeat this process to enter the second through fourth digits of the number. Once all four numbers have been entered, press Select again.
  5. This will unlock the keypad.
  6. If the code is incorrect, the screen will flash the lines “”–“”.
  7. Press Back to go back a step to enter the correct number and press Select.

If these above steps failed to resolve your query then follow this guideline. Click here

Note: In addition to troubleshooting thermostat errors, a complete list of the best Honeywell pro series with features and which one you should buy.

Before getting a help from thermostat manual or from professional a quick overview of what you should do to fix the issue by following these steps:

For Programmable Honeywell Thermostat Troubleshooting

In case the display is blank:

  • Replace batteries
  • Check circuit breaker
  • Ensure all panel doors of the indoor unit are closed
  • Verify power connection to furnace or AC unit by checking switch near indoor unit

If the display is on but heating/cooling isn’t working:

  • Verify date/time settings and temperature programming
  • Check wires and jumper settings after removing cover (e.g., “HE” for electric furnace, “HG” for gas furnace)
  • Test analog thermostat by adjusting temperature and waiting
  • If above steps don’t work, contact HVAC repair company.

For Smart Thermostat Troubleshooting

Smart thermostats have a significant advantage of providing error codes in case of an issue.

The following error codes require service:

  • 164: Heat pump requires servicing
  • 168: Wi-Fi radio error
  • 170: Internal memory error
  • 173: Error with thermostat temperature sensor
  • 177: Error with indoor temperature sensor
  • 178: Error with outdoor temperature sensor

Error codes that can be resolved by the user include:

  • 171: Set date and time to schedule the thermostat
  • 181/182: Replace air filter
  • 183: Clean the humidifier tank and replace the filter
  • 185: Replace the dehumidifier filter
  • 388: Register online for remote access and exterior temperature
  • 399: No internet connection
  • 400: Weak Wi-Fi signal
  • 508: Wi-Fi not connected

Honeywell Thermostat not Cooling Why and How to fix it?

If your Honeywell thermostat is not cooling, there could be several reasons for this issue. Here are some steps you can take to diagnose and potentially fix the problem:

  1. Check the Thermostat Settings:

    • Make sure the thermostat is set to “Cool” mode. Sometimes, it may accidentally be set to “Heat” or “Off.”
  2. Check the Temperature Setting:

    • Ensure that the temperature setting on the thermostat is set lower than the current room temperature. If it’s set higher, the air conditioner will not turn on.
  3. Check the Power:

    • Ensure that the thermostat has power. If it’s a battery-powered thermostat, replace the batteries and see if that resolves the issue. If it’s wired to your HVAC system, check the circuit breaker or fuse box to ensure power is reaching the system.
  4. Check the HVAC System:

    • Verify that your air conditioner is functional. Check if the outdoor unit is running, and listen for any unusual noises or vibrations. If the outdoor unit is not running, there may be an issue with the compressor or electrical connections. In such cases, you may need to contact a professional HVAC technician for repairs.
  5. Clean or Replace Air Filters:

    • Dirty or clogged air filters can restrict airflow, reducing the cooling efficiency of your HVAC system. Check and clean or replace the air filters if necessary. Dirty filters can also cause the evaporator coil to freeze, leading to reduced cooling performance.
  6. Check for Ice:

    • If you notice ice buildup on the indoor evaporator coil or refrigerant lines, turn off the AC and let it thaw completely. This can happen due to restricted airflow or low refrigerant levels. If it continues to happen, it’s best to call a professional technician to diagnose and repair the issue.
  7. Inspect Air Vents and Registers:

    • Ensure that all air vents and registers in your home are open and unobstructed. Blocked vents can limit the distribution of cool air.
  8. Thermostat Location:

    • Make sure the thermostat is not exposed to direct sunlight, drafts, or heat sources, as this can affect its temperature readings and cooling control.
  9. Check the Wiring:

    • Inspect the wiring connections at both the thermostat and the HVAC system. Loose or damaged wires can disrupt communication between the thermostat and the cooling system.

        10. Schedule Professional Maintenance:

  •       If you’ve tried the above steps and your thermostat still isn’t cooling, it’s a good idea to schedule                      professional HVAC maintenance.

Honeywell Thermostat not Turning on

If you’re facing issues with your Honeywell thermostat not turning on, it’s important to check for power supply problems, such as dead batteries or tripped circuit breakers. Additionally, ensure that the thermostat settings are correct for your cooling or heating needs. If the problem persists, consider professional assistance to diagnose and resolve any underlying issues with your HVAC system.


Honeywell Thermostat Heat Not Working On Auto

The auto settings on your thermostat might not work if there are problems with the wiring. Fix bugs and glitches in the software to change auto settings. On the other hand, your thermostat’s battery could be dying, the sensor might not be working, or the feature might not be on. it is not possible to explain in detail here, therefore a complete researched topic on this particular issue for the user to benefit from it. 

Honeywell Pro Series Thermostat Manual

Honeywell Thermostat Helpline for the United States

Thermostats, Furnace Filters, and Whole House Humidifiers 800-468-1502  
Wi-Fi Digital Thermostats 855-733-5465

Honeywell Thermostat Helpline for International Customers:

International: 001 (480) 353-3020

Hours: 4:00 a.m. Monday through 11 a.m. Saturday (GMT) 

If you need Honeywell thermostat help from their Support… Then Click Here or get help from outside service experts.

Frequently Asked Questions:

Is There A Reset Button On A Honeywell Thermostat?

The location and design of the reset button on a Honeywell thermostat can vary depending on the model you have. Some Honeywell thermostats have a small reset button located on the thermostat itself, often behind the thermostat’s cover. This button is usually labeled “Reset” or “System Reset.”

What Happens If I Push The Reset Button On My Thermostat?

Pushing the reset button on a thermostat will clear any current settings or programming and return the thermostat to its factory defaults. This may include thermostat temperature settings, schedule programming, and other preferences. It is typically used as a troubleshooting step when the thermostat is not working correctly or as a way to clear settings before reprogramming the thermostat.

What does a failed thermostat look like?

A failed thermostat can display several signs, including:

  1. Inaccurate temperature readings: The thermostat may display a temperature that is different from the actual room temperature.
  2. Inconsistent performance: The thermostat may turn on and off unexpectedly, or fail to turn on at all.
  3. No display: The thermostat may have no display or the display may be blank.
  4. Dead batteries: A battery-operated thermostat may display a low battery warning or not turn on at all if the batteries are dead.
  5. Thermostat Errors messages: Some thermostats may display error messages or flashing lights indicating a problem.
  6. Physical damage: In some cases, a thermostat can have physical damage such as broken wires or loose connections.
  7. Inability to change settings: Some thermostats may not allow you to change the temperature or settings, indicating a failure in the control system.

Why is my Honeywell Pro Series not Working?

Replace the batteries; inspect the circuit breaker; Check that all of the panel doors on the indoor unit are closed. Check the switch near the interior unit to ensure that electricity is connected to the furnace or air conditioning unit. and in the last perform a hard reset. if nothing works call an expert.

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13 thoughts on “Honeywell Pro Series Thermostat Troubleshooting”

  1. After a new pair of fresh AA batteries are correctly installed to replace the old ones when Low Battery Icon showed, thermostat still shows Low battery icon. What could the problem? Thanks

  2. After a new pair of fresh AA batteries are correctly installed to replace the old ones when Low Battery Icon showed, thermostat still shows Low battery icon. What could the problem? Thanks

    1. H Automations

      reset it and see if it works.. otherwise get recommended batteries for this device.. and then reset it..

  3. William Artesani

    I have a 6 month old Honeywell Thermostat T4 Pro, that was installed when a a new central A/C system was installed. It worked fine for a month or two, my problem is that it changes the temp I set , for example I set the cooling temp @ 72 at night, it will run OK for a few hours then change my set temp to 76, or 82, or 85 etc, so the A/C shuts off, it never changes to a lower temp. The same thing happens when it is set for 76 during the day. I replaced the batteries to no avail. How do I correct this, or is the thermostat defective?

  4. I have a Honeywell pro series thermostat. I’m trying to sinc it with my cell phone. One of the first steps is to press and hold the screen however when i do that nothing happens. ??

  5. Honeywell home pro series. Screen reads two or three degrees high than actual room temperature. We have checked using several different thermometers.

  6. Wizzdom DOKUBO


  7. I have my Honeywell pro series thermostat on cool and it won’t let me go lower than 68 degrees on one zone. My other zone, still a Honeywell Pro series will let me go down below 69 degrees. Can’t figure out the issue.

  8. Jeff Ruggaber

    Honeywell T 6 Pro, screen is black. Furnace still running. Checked WiFi, power support, furnace door all good. Removed device for 15 minutes and put back on. Nothing.

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