Furnace shows sensor open-circuit error, temperature reading extremely low or missing

Safety first: Turn off power before handling wiring.

• Check connector: Ensure the sensor plug is fully seated on the PCB and at the sensor body.
• Continuity test: With power off, disconnect the sensor and measure resistance across its terminals. Infinite resistance indicates an open sensor.
• Inspect cable: Look for breaks where the cable passes through grommets or around sharp edges.
• Replace sensor: Install a new Roca sensor and secure the cable to prevent future damage.

Warning: Do not operate the furnace with sensors disconnected or bypassed.