Thermostat displays E1 and will not control heating or cooling

Safety first: Turn off power to the HVAC system at the breaker before removing the thermostat from the wall. Low-voltage circuits can still short and damage the thermostat or furnace control board.

• Power down: Switch off the furnace/air handler breaker and any dedicated thermostat transformer breaker.
• Remove thermostat: Gently pull the Lux smart thermostat straight off its wall plate. Do not twist excessively to avoid damaging pins.
• Inspect for damage: On the back of the thermostat, locate the small room temperature sensor (usually a tiny bead or SMD component near the air vent slots). Check for obvious cracks, broken solder joints, or corrosion.
• Clean contacts: Use a dry, soft brush or compressed air to remove dust from the sensor area and the pogo-pin contacts that mate with the wall plate.
• Reset thermostat: With the thermostat removed, wait 2–3 minutes, then reinstall it on the wall plate and restore power. Perform a factory reset following the Lux user manual.
• Test operation: If E1 clears and temperature readings look normal, monitor for recurrence. If E1 returns, the internal sensor on the main PCB is likely failed and the thermostat must be replaced.

Do not attempt board-level solder repair unless you are qualified; replacing the thermostat is the recommended remedy.