Safety first: Isolate electrical power before accessing the control compartment.

Locate the flow NTC: On most Roca furnaces, the flow temperature sensor is clipped or inserted into a pocket on the flow pipe leaving the heat exchanger.
Inspect wiring: Check the two-wire harness from the NTC to the control board. Ensure the plug is fully seated and wires are not cut or pinched.
Check sensor seating: Make sure the sensor is firmly in contact with the pipe or fully inserted into its well, with thermal paste if originally fitted.
Basic resistance check (for skilled users): With power off and wires disconnected, measure resistance across the NTC with a multimeter. Compare to Roca’s temperature/resistance chart. A reading of infinite (open) or near zero (short) indicates a bad sensor.
Replace if faulty: If the sensor is defective, replace it with the exact Roca-specified NTC for your model.

Warning: Do not bypass or short temperature sensors; this can cause dangerous overheating.

Furnace shows a temperature sensor error, may run briefly then shut down, or not start at all

Possible Causes