E20 error; unit may show a lock icon and ignore button presses.

Safety first: If the unit is unresponsive but safe, you may leave it plugged in while attempting unlock procedures. For disassembly, unplug first.

• Step 1 – Attempt manual unlock: Press and hold the LOCK or designated key combination (refer to Teendow manual, often 3–5 seconds) to toggle the control lock.
• Step 2 – Power cycle: Unplug the unit for 5 minutes, then plug back in and immediately attempt the unlock sequence.
• Step 3 – Inspect keypad: If still locked, remove the control panel and inspect the keypad or touch board for moisture or contamination. Clean and dry thoroughly.
• Step 4 – Check ribbon cable: Reseat the ribbon cable between the keypad and UI logic board.
• Step 5 – Replace UI board: If the lock state cannot be cleared and E20 remains, replace the user interface board with a Teendow-compatible part.