Thermostat shows E13 and indicates internal clock or schedule error; timed programs may not run correctly.

Safety first: Disconnect power before opening the thermostat housing. Do not attempt component-level repair unless qualified.

Steps to diagnose and fix:

• 1. Reset date and time: In the thermostat menu or app, manually set the correct date and time. Observe whether the clock drifts or resets after a short power loss.
• 2. Check for firmware updates: Use the Danfoss app or service interface to update the thermostat firmware to the latest version, which may correct RTC issues.
• 3. Inspect backup power component: Some models use a small coin cell or supercapacitor to maintain time. If accessible and user-replaceable, install a new component of the same type and rating.
• 4. Minimize power interruptions: Ensure the thermostat is on a stable circuit that is not frequently switched off. Avoid turning off power at the breaker for extended periods.
• 5. Replace thermostat if RTC hardware failed: If E13 persists and the clock cannot keep time, the RTC circuit on the PCB is likely defective. Replace the thermostat.

When to call a professional: For units under warranty or where the backup component is soldered, contact Danfoss service or your installer.