T4 Pro thermostat. Why can't I set it to cool?

Do you mean the alert flag (a triangle with an exclamation inside it) or a different symbol? The Alert flag will appear with another message on the screen. If it is time to replace the battery, you'll also see "BATT" to the left of the flag and a low battery icon somewhere along the top of the LCD screen. If the thermostat is set to alert you to change the HVAC system filter regularly, you'll see "REPL" to the left of the alert flag.

This is from the T4 Pro thermostat manual on pages 6 and 7. See https://forwardthinking.honeywellhome.com/assets/tseries/resources/install/T4%20Pro%20User%20Guide%20-%2033-00188EFS.pdf . The T6 Pro uses the same alert behavior.

I hope this helps.

Cindy Wells

you need to change the settings to make it programmable. the setting is off, read the manual

press and hold center and + buttons for 3 seconds. Then select select until option 435. This should be set at 0.

If you need further help, reach me via phone at https://www.6ya.com/expert/thomas_092728000e6acb79

Help how do I unlock this?

didnt specify to much --generic answer -- sounds like hooking up a heating or cooling unit black and white should be your line voltage use a meter to test your black and white line for 110v if motor is 110v the low voltage lines are control or switch lines that dont go to motor they usually go to a thermostat or transformer

Lower temperature to lowest setting wait 1 1/2 to two min U should hear a click at thermostat & it should come on.

Right below the w setting on the base plate is the o/b connection. Put the O wire in this slot. During the initial test for heat and cool, the bias for cool for function 2 is 0 and for heat it is 1. To reach the programming press fan and Up arrow. Press next to reach function 2. Be aware the the O wire is energized and operates the reversing valve. Some manufacturers energizes the reversing valve to go into cooling, and some leave it deenergized to be in cooling. Select either 0 or 1 to make the system perform in the correct mode.
Hope this helps.

I have T4 RF wireless thermostat.When you turn off heating from thermostat,for some reasons after 1 hour boiler kick on and radiator feel hot again.please give me solution.

Remove the front cover off the thermostat and jumper the power wire= r- to g==fan & r-to y==cool if it works, then its the thermostat!