Thermostat display shows E01 and heating/cooling outputs are disabled.

Safety first: Turn off power to the HVAC system and thermostat at the circuit breaker before removing the thermostat from the wall.

Steps to check:

• Remove the thermostat from its wall mounting plate by gently pulling it straight out (do not twist excessively).
• Inspect the main PCB for obvious damage near the internal temperature sensor (usually a small bead or SMD NTC labeled NTC or TH).
• Use a multimeter (if available) to measure resistance across the internal NTC sensor pads; compare to Schneider Electric service documentation for expected values at room temperature. An open (infinite) or near-zero reading indicates a failed sensor.
• Power-cycle the thermostat: restore power for 30 seconds, then cut power again and wait 2 minutes before turning it back on. Sometimes E01 clears after a reset if it was triggered by a transient fault.
• If the error persists and the sensor is clearly damaged or out of spec, the internal sensor is not field-replaceable on most Schneider Electric smart thermostats; the entire thermostat head unit (display module) typically must be replaced.

When to call a professional: If you are not comfortable opening the thermostat or using a multimeter, or if the unit is under warranty, contact a Schneider Electric authorized service provider for a replacement thermostat module.