how do i get the t9 to follow my remote sensor instead of the thermostat's own temperature?

Diagnosis

The Honeywell Home T9 utilizes a "Comfort Profile" system rather than a global temperature override. The root cause of your issue is that the T9 is currently configured to use the internal thermistor located inside the wall-mounted thermostat chassis. Because the T9 supports multiple remote sensors, it does not automatically switch to a remote reading just because the sensor is paired and online; it requires a specific assignment within each individual operational mode (Home, Away, Sleep, etc.). If the thermostat is ignoring your remote sensor, it is because the "Temperature Source" for the active profile is still set to "Thermostat." You can confirm this by looking at the main screen: if the temperature displayed is the one from the wall unit despite the remote sensor showing a different temperature in the app, the profile is not correctly mapped. This often happens after a factory reset or when adding a new sensor after the initial setup process.

How to Fix It

To force the T9 to prioritize a remote sensor over the internal thermostat reading, follow these precise steps on the device screen:

1. Tap the Menu icon on the bottom right of the home screen.
2. Select Comfort Profiles from the list of options.
3. You will see a list of profiles (e.g., Home, Away, Sleep). Tap on the specific profile that is currently active or the one you wish to modify.
4. Locate the section labeled Temperature Source. You will see "Thermostat" currently selected with a checkmark.
5. Tap the Thermostat option to open the list of available sensors.
6. Select the specific Remote Sensor name (e.g., "Bedroom" or "Living Room") that you want the system to follow.
7. If you want the system to average the temperature between the wall unit and the sensor, select the Average option from this same list.
8. Tap Done or the back arrow to save the changes.
9. Repeat this entire process for every profile you use (Home, Away, and Sleep) to ensure the sensor is followed regardless of the time of day.

If That Didn't Work

• Verify Sensor Connectivity: Check the "Sensors" menu in the Honeywell Home app. If the sensor shows as "Offline" or has a low battery warning, the thermostat will automatically revert to the internal sensor to prevent the HVAC system from failing to trigger. Replace the CR2032 battery and wait 5 minutes for it to reconnect.
• Check for Signal Interference: If the sensor is more than 60 feet away or separated by thick masonry/metal studs, the T9 may lose the handshake. Move the sensor closer to the thermostat temporarily; if the temperature source suddenly becomes available in the menu, you have a range issue.
• Perform a Sensor Re-Pair: Go to Menu > Sensors and delete the problematic sensor. Remove the battery from the sensor for 30 seconds, reinsert it, and then use the "Add Sensor" function on the T9 to re-establish the encrypted link.
• Update Firmware: Ensure your T9 is connected to a 2.4GHz Wi-Fi network. Firmware updates often resolve bugs where the UI indicates a sensor is selected, but the logic board continues to pull data from the internal thermistor.

Heads Up

• Battery Life: Remote sensors typically last 1-2 years, but if you have them in high-humidity areas (like a bathroom), the CR2032 batteries can drain significantly faster due to surface leakage.
• Placement Warning: Do not place remote sensors within 3 feet of a supply vent, window, or lamp. This will cause "ghost readings" and lead to your HVAC system overrunning or short-cycling.
• Averaging Logic: When using the "Average" setting, the T9 calculates the mean of the internal sensor and the remote. If your wall unit is in a drafty hallway and your sensor is in a warm bedroom, the average may never actually reach the set point of either room.
• App Sync: Changes made on the physical T9 screen sync to the app, but occasionally there is a lag. Always verify the "Temperature Source" on the physical device for the most accurate confirmation.