Thermostat shows E12 and one or more remote room sensors are missing or reading incorrectly

Safety: Turn OFF power to the HVAC system at the breaker before working on low-voltage sensor wiring.

• Identify sensor: Determine which remote room sensor is reporting the fault (often indicated by zone or room name in the thermostat menu).
• Inspect sensor wiring: Remove the sensor cover and check that the wires are securely attached to the sensor terminals. At the thermostat or zone panel, verify the corresponding sensor terminals are tight.
• Check for damage: Follow the sensor cable as far as accessible, looking for staples through the wire, crushed sections, or splices. Repair or replace damaged cable.
• Resistance test: With power OFF, disconnect the sensor and measure its resistance. Compare to the Ruud sensor chart for the room temperature. Replace the sensor if readings are far out of range.
• Configuration: In the thermostat settings, ensure the sensor is enabled and assigned to the correct zone or averaging group.
• Retest: Restore power and verify that E12 clears and the sensor temperature displays correctly.