Generic 'Er' or 'Err' message on display; thermostat does not follow commands or schedule.

Safety first: For mains‑powered units, isolate power before removing from the wall. For battery units, remove batteries.

Steps:

• Soft reset: Remove power for 2–3 minutes, then restore. Check if the error clears.
• Factory reset: Perform a factory reset according to the Danfoss Ally manual (usually a specific button combination). This will erase schedules and pairing.
• Re‑add to Ally system: In the Ally app, delete the old device entry, then add the thermostat again and complete configuration.
• Update firmware: Check for firmware updates via the Ally app and apply them.
• Replace if recurring: If the generic error returns repeatedly after reset and update, the internal memory or processor is likely faulty; replace the thermostat.