the app says my thermostat is offline but the screen on the wall is working fine and shows it's connected.

Diagnosis

This discrepancy occurs because the RTH9585WF operates on two distinct communication planes: the local control plane and the cloud connectivity plane. When the wall unit shows a "connected" icon, it is confirming a successful handshake with your local wireless router (DHCP assignment). However, the "Offline" status in the Total Connect Home or Honeywell Home app indicates a failure in the WAN (Wide Area Network) tunnel between your router and the Honeywell cloud servers. This "ghost connection" typically happens due to a stale DNS cache in the router, a temporary IP conflict where the thermostat is holding an expired lease, or a firewall rule that has suddenly flagged the thermostat's outbound port (usually port 80 or 443) as suspicious. Because the thermostat's onboard WiFi chip remains linked to the router, the screen doesn't trigger a "Disconnected" alert, even though no data is actually reaching the app.

How to Fix It

To resolve the synchronization gap, you must force a fresh handshake between the device, the router, and the cloud server. Follow these steps in this exact order:

1. Power Cycle the Network: Unplug the power cable from your modem and your wireless router. Wait exactly 60 seconds to allow the capacitors to discharge. Plug the modem in first and wait for the "Internet" or "Online" LED to turn solid green. Then, plug in the router and wait 3 minutes for the local network to fully stabilize.
2. Hard Reset the Thermostat Connection: On the RTH9585WF wall unit, press the Menu button. Navigate to WiFi Setup and select Disconnect. This clears the current local IP lease.
3. Re-establish Connection: In the same WiFi Setup menu, select Connect. Choose your 2.4GHz network SSID from the list. Enter your password carefully; remember that this model is sensitive to special characters in passwords.
4. Verify Cloud Sync: Once the screen confirms "Connected," wait 2 minutes. Open the app on your mobile device, swipe down to refresh the dashboard, and check if the status changes from "Offline" to "Online."

If That Didn't Work

• Switch to a Static IP: Access your router's admin panel (usually 192.168.1.1 or 192.168.0.1) and locate the DHCP client list. Find the RTH9585WF and assign it a "Reserved IP" or "Static IP." This prevents the router from assigning the thermostat's address to another device, which is a common cause of intermittent app disconnects.
• Toggle 2.4GHz Bandwidth: The RTH9585WF does not support 5GHz networks. If you have a "Dual-Band" or "Smart Connect" router that merges both bands into one SSID, the thermostat may be attempting to jump to a frequency it cannot maintain. Split your bands into two separate SSIDs (e.g., "Home_WiFi" and "Home_WiFi_5G") and force the thermostat to connect only to the 2.4GHz band.
• Check DNS Settings: If the device is connected to the router but cannot reach the cloud, change your router's DNS settings from the ISP default to Google's Public DNS (Primary: 8.8.8.8, Secondary: 8.8.4.4). This often resolves routing issues to Honeywell's specific server clusters.
• Perform a Factory Reset: If all else fails, go to the Menu on the thermostat, select Reset, and choose Factory Reset. You will need to re-add the device to your app account using the MAC address found on the back of the thermostat faceplate.

Heads Up

• Avoid 5GHz: Never attempt to connect this model to a 5GHz network; it will either fail to connect or will frequently drop the signal, leading to the "Offline" app error.
• Signal Strength: Ensure your router is not blocked by large metal objects or mirrors between the router and the thermostat, as the RTH9585WF has a relatively small internal antenna.
• Firmware Updates: When the device is online, do not power cycle it for at least 24 hours. Honeywell often pushes firmware updates silently in the background; interrupting this process can cause a "boot loop" or permanent connectivity failure.