the schedule on my t9 just randomly changes or doesn't run, even though i set it up in the app.

Diagnosis

The Honeywell Home T9 is a cloud-dependent system, meaning the logic for your schedule resides on Honeywell's servers rather than locally on the thermostat hardware. When a schedule "randomly" changes or fails to trigger, it is almost always a synchronization conflict between the Resideo/Honeywell Home app and the T9 wall unit. This happens when a manual temperature override is performed on the device, which creates a "Hold" state that suppresses the programmed schedule until the next scheduled transition point. Furthermore, the T9 features aggressive automation logic. If Geofencing is enabled, the thermostat ignores the time-based schedule entirely in favor of location-based triggers. If your phone's GPS drifts or if you have multiple users assigned to the home, the system may trigger an "Away" or "Arriving" state that overrides your set points. You can confirm this by looking at the T9 screen; if it displays "Following Schedule" it is working, but if it says "Holding" or "Away," the app-based schedule is being intentionally bypassed by a priority override.

How to Fix It

To resolve the synchronization issues and restore your schedule, follow these exact steps to clear the logic cache and reset the priority settings:

1. Open the Honeywell Home app and navigate to the Devices menu. Select your T9 thermostat.
2. Tap the Schedule icon. Look for any active "Holds." If the screen shows a manual temperature override, tap Remove Hold or Run Schedule to force the device back into its programmed routine.
3. Enter the Settings menu (gear icon) and locate Geofencing. Toggle this switch to OFF. Even if you want this feature, disabling it temporarily is necessary to confirm the schedule works without location interference.
4. Check the Away Mode setting. Ensure it is not set to "Always Away" or triggered by a secondary user's phone.
5. Perform a "Hard Sync": Go to the physical T9 thermostat on the wall. Press the Menu button, navigate to Settings, and select Reset. Choose Network Reset (this will not delete your schedule, but it forces the device to re-handshake with the cloud server).
6. Once the device reconnects to Wi-Fi, wait 5 minutes for the server to push the current schedule from the app to the local hardware.

If That Didn't Work

• Verify Time Zone Settings: If the thermostat's internal clock is offset from your phone's time zone, the schedule will run, but at the wrong time. In the app, go to Settings > Device Settings and verify the Zip Code and Time Zone are exactly correct. A mismatch here often makes it look like the schedule "isn't running" when it is actually just running 1-2 hours off.
• Check for Conflicting Smart Room Sensors: If you have T9 wireless room sensors installed, check the Priority setting. If the thermostat is set to "Average" or "Follow" a specific sensor that is located in a drafty area or near a heat source, the T9 may adjust the temperature to satisfy that sensor, overriding your desired set point. Change the priority to "Thermostat Only" to see if the schedule stabilizes.
• Update Firmware: Outdated firmware on the T9 can cause "ghost" overrides. Ensure your Wi-Fi signal strength at the wall is at least -65dBm. If the signal is weak, the device may miss the "trigger" command from the cloud server to change temperatures.
• Factory Reset and Re-pairing: As a last resort, remove the device from the app entirely and perform a full factory reset via the wall unit menu. Re-add the T9 to the app as a new device. This clears corrupted local cache files that often cause scheduling loops.

Heads Up

• Avoid Manual Overrides: Touching the temperature arrows on the wall unit creates a "Hold" that lasts until the next scheduled event. To avoid this, use the app to adjust temperatures.
• Battery Maintenance: Ensure your T9 sensors have fresh batteries. A low-battery sensor can send erratic temperature readings that trigger the thermostat to override the schedule to compensate.
• C-Wire Requirement: The T9 requires a constant 24V C-wire. If you are using a power extender kit or a "phantom" power setup, voltage drops can cause the Wi-Fi chip to reboot, leading to missed schedule transitions.
• App Version: Always ensure you are using the latest version of the Resideo app, as Honeywell has transitioned many T9 features from the old "Total Connect Comfort" platform to the newer Resideo ecosystem.