Display shows E05, furnace stops heating, may occur intermittently during operation.

Safety: Isolate electrical power before accessing the control compartment.

Steps:

• Locate the flow sensor: On Cointra furnaces, the flow NTC is usually clipped to the flow pipe leaving the heat exchanger. Identify the small probe with two wires.
• Check connections: Ensure the NTC sensor plug is fully seated on the control board and that the wires are not damaged or pinched.
• Inspect sensor body: Look for signs of moisture ingress, corrosion, or physical damage. If the sensor is loose from the pipe, reattach it firmly with its clip and ensure good thermal contact.
• Basic resistance check (if you have a multimeter): With power off, disconnect the sensor and measure its resistance. Compare to Cointra's temperature/resistance chart (e.g., around 10 kΩ at 25°C for many NTCs). If reading is open, shorted, or far off, replace the sensor.

Professional service: If a new NTC does not clear E05, the control board's sensor input may be defective and should be tested and replaced by an authorized technician.