The furnace shuts down with error A7; the burner stops, and hot water and heating are unavailable.

Safety first: Switch off the furnace at the main switch and isolate it from the mains. Allow the appliance to cool.

• 1. Locate the flow NTC: On most Junkers furnaces, the flow temperature sensor is clipped or screwed into the flow pipe leaving the heat exchanger. Refer to the appliance data plate and service manual for the exact location.
• 2. Visual inspection: Check the sensor body and wiring for signs of overheating, moisture ingress, or mechanical damage. Ensure the connector is fully seated on the sensor and on the main PCB.
• 3. Clean and reseat connectors: Disconnect the NTC plug with power off. Inspect for corrosion or bent pins. Clean lightly with electrical contact cleaner and reconnect firmly.
• 4. Resistance check: Using a multimeter, measure the NTC resistance at room temperature and compare it with the Junkers specification (typically in the range of several kΩ at 20°C). If the reading is open circuit, shorted, or far out of range, replace the sensor.
• 5. Wiring continuity: If the sensor tests OK, check the continuity of the cable from the NTC to the control board. Repair or replace the harness if broken.
• 6. Control board: If the sensor and wiring are correct but A7 persists, the main control board may be defective and should be tested and replaced by a qualified technician.