Furnace shuts down with A7, burner stops, hot water and heating unavailable

Safety first: Switch off the furnace at the main switch and isolate 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 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 with 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 continuity of the cable from the NTC to the control board. Repair or replace the harness if broken.
• 6. Control board: If 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.