my honeywell t9 keeps saying temperature setting not allowed, can't set it below 70

Diagnosis

This error occurs because the Honeywell Home T9 (RCHT9610WFSW2003) has an active "Temperature Setpoint Limit" configured in the Advanced Setup menu. While the hardware has absolute hard limits (50°F for cooling), the "Temperature Setting Not Allowed" message specifically triggers when a user-defined software restriction is in place. This is often a remnant of a previous installer's settings or a safety configuration intended to prevent pipes from freezing or to stop the AC from over-cooling a room to an uncomfortable level. You can confirm this is a software limit rather than a hardware failure by attempting to raise the temperature; if the thermostat allows you to move the setpoint up to 75°F but blocks you at exactly 70°F when moving down, the "Minimum Cooling Setpoint" or "Minimum Heating Setpoint" has been locked. This is distinct from a system malfunction; the thermostat is functioning exactly as programmed, but the program is too restrictive for your current needs.

How to Fix It

To remove or adjust these limits, you must access the Advanced Menu, which is hidden from the standard user interface to prevent accidental changes. Follow these exact steps:

1. Wake the thermostat by touching the screen.
2. Press the Menu icon on the home screen.
3. Scroll down and select Advanced Setup.
4. Navigate through the list of settings until you find Temperature Setpoint Limits (this may be listed as "Min/Max Setpoints" depending on your firmware version).
5. Select Cooling Min. You will see the current value set to 70°F.
6. Use the Down Arrow or the numeric keypad to lower this value. For maximum flexibility, set this to 50°F.
7. Press Done or the checkmark to save the change.
8. Repeat the process for Heating Min if you are experiencing similar issues in Heat mode, setting it to 40°F.
9. Exit the menu by pressing the Home button. You should now be able to slide the temperature dial below 70°F without the error message appearing.

If That Didn't Work

• Check for "Lock" Mode: If the Advanced Setup menu is password protected or grayed out, your thermostat is in Lock Mode. You will need to enter the 4-digit installer code (default is often 0000 or 1234) to unlock the settings before you can modify the temperature bounds.
• Verify the "Auto" Changeover: If your system is set to "Auto" instead of "Cool" or "Heat," the T9 enforces a "Deadband" (a gap between heating and cooling setpoints). If your heating limit is 70°F and your cooling limit is 72°F, you will have very little room to move. Switch the system mode specifically to Cool to see if the limit persists.
• Reset to Factory Defaults: If the software limits are corrupted or you cannot find the specific setting, go to Menu > Advanced Setup > Factory Reset. This will wipe all custom limits and return the T9 to its default range of 50°F–99°F, though you will have to reconnect it to your Wi-Fi and the Honeywell Home app.
• Check App-Based Restrictions: If you are using the Resideo/Honeywell Home app, check if a "Geofencing" or "Schedule" override is active. Sometimes the app pushes a "Hold" command that overrides manual adjustments on the wall unit, triggering the "Not Allowed" message when you try to deviate too far from the scheduled setpoint.

Heads Up

• Avoid Extreme Lows: Do not set your cooling minimum to 50°F unless you have a high-efficiency system; setting the thermostat too low in humid conditions can cause the evaporator coils to freeze, leading to a total system shutdown.
• C-Wire Stability: Ensure your C-wire is securely fastened to the RC/RH terminals. Intermittent power drops can sometimes cause the T9 to reboot into a "Safe Mode" where certain setpoint ranges are restricted.
• Firmware Updates: Keep your T9 updated via the app. Early versions of the RCHT9610WFSW2003 firmware had bugs regarding setpoint persistence after power cycles.