Furnace shows A9 and stops, heating and hot water unavailable

Safety first: Turn off power and close the cold water inlet if you need to remove any DHW components. Allow the unit to cool.

• 1. Locate DHW NTC: On combi-type Junkers furnaces, the DHW temperature sensor is usually mounted on the DHW outlet pipe or integrated into the plate heat exchanger assembly.
• 2. Visual check: Inspect the sensor body for scale, corrosion, or leaks. Check that the connector is firmly attached and dry.
• 3. Electrical test: Disconnect the sensor and measure its resistance at room temperature. Compare with the Junkers NTC chart. If the value is not within the expected range, replace the DHW NTC.
• 4. Wiring inspection: Trace the cable from the sensor to the main PCB. Look for pinched, cut, or overheated sections. Repair or replace the harness if damaged.
• 5. Reassemble and test: Refit the sensor with new thermal paste or sealing washer if required. Restore power, reset the appliance, and run a hot water draw-off to confirm correct operation.
• 6. Professional help: If the error persists with a known-good sensor and wiring, the control board may be defective and should be replaced by a qualified technician.