Thermostat shows E20 and reports schedule or clock synchronization error

Safety first: No hazardous work is required for this issue.

• Step 1 – Check internet connection: Ensure the thermostat is connected to Wi‑Fi and has internet access so it can sync time with servers.
• Step 2 – Manually set time: In the thermostat settings, manually set the correct time, date, and time zone. Save and observe if E20 clears.
• Step 3 – Verify backup power: For models with backup batteries, ensure the battery is installed and in good condition so the clock can ride through brief outages.
• Step 4 – Firmware update: Install any available firmware updates, as time sync bugs are often corrected in software.
• Step 5 – Replace thermostat: If the internal clock cannot keep time even with stable power and E20 persists, the real‑time clock circuit may be defective and the thermostat should be replaced.