Honeywell Pro Series Thermostat Troubleshooting

Here is the compilation of a few of the most problems questions by Honeywell pro series thermostat users and how to troubleshooting against them are in detail.

So here are Honeywell Pro Series Thermostat Troubleshooting

Honeywell Thermostat Troubleshooting No Display

  • Check circuit breaker and reset if necessary.
  • Make sure power switch for heating & cooling system is on.
  • Make sure 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 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.

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 circuit breaker and reset if necessary.
  • Make sure power switch for heating & cooling system is on.           
  • Make sure 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 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 program option

  • From home screen, press 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 may have been configured as non-programmable by the installer.

Then Check ISU Settings

  1. Press and hold CENTER and + buttons for approximately 3 seconds to enter 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 ISU menu screen to continue editing another setup option.
  6. To finish setup process and save your setting, press Home and return to Home screen.

Temperature settings do not change

  • If 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 mode button to set system)
  • If you are 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.

How to unlock/lock Honeywell Pro thermostat

The thermostat 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.

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

Honeywell Pro Series Thermostat Manual

6 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

  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.

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