Honeywell T8665A1002 - Digital Thermostat, 3h User Manual (English)

Questions and Answers:

A
Ashley HarrisJul 30, 2025
Why is my Honeywell T8665A1002 - Digital 3h not turning on the heat?
- T
  Timothy RobinsonJul 31, 2025
  If your Honeywell thermostat isn't turning on the heat, it could be due to several reasons. First, make sure that the system selection is set to Heat and that the heating setpoint is higher than the current room temperature. Also, check the circuit breaker and fuse box for any tripped breakers or blown fuses, and reset or replace them as needed. Verify that the System switch on the equipment is in the On position. After making these adjustments, allow five minutes for the system to respond. The thermostat may display “Wait” during this time.
S
Stephanie RobinsonAug 5, 2025
Why is my Honeywell Thermostat not turning on the cooling?
- C
  cunninghamjeremyAug 5, 2025
  If your Honeywell thermostat isn't activating the cooling, it might be because the system selection isn't set to Cool, or the cooling setpoint is above the room temperature. Ensure the setpoint is below room temperature. Check the circuit breaker and the fuse box; reset the breaker if it's tripped or replace the fuse if it's blown. Also, confirm that the System switch at the equipment is in the On position. After making these checks, allow five minutes for the system to respond (the thermostat may display “Wait”).
B
Brian SmithAug 12, 2025
What to do if my Honeywell Thermostat display does not come on?
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  Thomas JohnsonAug 12, 2025
  If the display on your Honeywell thermostat isn't turning on, the thermostat might not be getting power. Check that the batteries are correctly installed. Also, make sure the thermostat is properly mounted and latched onto the wallplate.
B
Bradley ReedAug 18, 2025
What does it mean when the "Filter" is flashing on my Honeywell T8665A1002 - Digital 3h Thermostat?
- M
  Maria JonesAug 18, 2025
  If the word "Filter" is flashing on your Honeywell thermostat's display, it means that the Filter Timer has expired. To resolve this, reset the timer.
T
Thomas GriffinAug 25, 2025
What to do if the system on indicator is lit on my Honeywell Thermostat, but there is no warm or cool air?
- K
  Keith KimAug 25, 2025
  If the system on indicator is lit on your Honeywell thermostat, but no warm or cool air is coming from the registers, it could be because the heating or cooling equipment turns on the fan when it has reached the preset time or temperature. Wait a minute after seeing the indicator and then check the registers. If there is still no hot or cool air, refer to the troubleshooting steps for 'Heating does not come on' or 'Cooling does not come on'.

Honeywell T8665A1002 - Digital Thermostat, 3h Specifications

General

Brand	Honeywell
Model	T8665A1002 - Digital Thermostat, 3h
Category	Thermostat
Language	English

Summary

Keyboard and Display Description

Keyboard

The keyboard is located behind the thermostat cover. Three frequently used keys, increase or decrease and i, are located next to the display. See Fig. 1.

Display

The thermostat displays important information such as day, time, schedule period, temperature, system and fan operation. See Fig. 2.

Operating Your Thermostat

Setting System and Fan Keys

Use the System and Fan keys to change the system and fan settings. The fan settings can be set for each schedule period individually. The system selection is for all the schedule periods.

Press the System key until the desired system (Heat, Off, Cool, or Auto) displays. Heat: controls heating. Off: both off. Cool: controls cooling. Auto: automatically changes between heating and cooling.