Display shows E05 and the furnace will not start; often associated with a sensor icon or abnormal temperature reading.

Safety: Isolate electrical power before accessing the control compartment of the Viadrus furnace.

• Read sensor value: On some Viadrus controls, the diagnostic menu will show the flow temperature. If it reads -40°C, 0°C, or an impossible value, the NTC is likely open or shorted.
• Inspect wiring: Locate the flow NTC sensor on the flow pipe or heat exchanger. Follow its cable to the control board. Check for cuts, crushed insulation, or loose plugs. Reseat the connector firmly.
• Measure resistance: With power off and sensor disconnected, measure the NTC resistance with a multimeter. Compare to the Viadrus temperature/resistance table (e.g., around 10 kΩ at 25°C for many NTCs). If the reading is infinite or near zero, replace the sensor.
• Check sensor pocket: If the sensor is inserted into a dry pocket, ensure it is fully seated and that there is no corrosion preventing good thermal contact. Replace the pocket if badly corroded.
• Control board: If the sensor tests good but E05 persists, the input circuit on the main control board may be damaged and require replacement by a technician.