Thermostat shows E10 and indicates internal hardware error; most functions are disabled.

Safety first: Disconnect power to the thermostat before removing it from the wall or backplate.

Steps to diagnose and fix:

• 1. Power-cycle the unit: Remove power for at least 1 minute, then restore. Sometimes transient faults clear after a full reboot.
• 2. Check for moisture or contamination: Remove the front cover and inspect for signs of water ingress, condensation, or corrosion. If present, the thermostat may be unsafe to use and should be replaced.
• 3. Attempt firmware update: If supported by your Danfoss model, use the app or service tool to update firmware to the latest version. Follow Danfoss instructions carefully and do not interrupt power during the update.
• 4. Inspect for physical damage: Look for burnt components, cracked PCB, or impact damage. Any such damage typically requires full replacement.
• 5. Replace thermostat: If E10 persists after reboot and firmware update, the internal electronics have failed. Replace the thermostat with an identical or compatible Danfoss smart thermostat.

When to call a professional: For warranty evaluation or if you suspect surge damage, contact Danfoss support or your installer.