Atlantic heat-pump water heater shows E9; unit may run briefly then shut down.

Safety: Turn off power before accessing the top module.

• Locate the ambient air sensor usually placed near the air intake grille of the Atlantic heat pump module.
• Ensure the sensor is not covered by insulation or debris and is exposed to room air.
• Measure its resistance and compare with the Atlantic NTC specification at the current room temperature.
• Replace the sensor if readings are incorrect or intermittent when moving the cable.
• Inspect the connector and harness back to the control board; repair or replace if damaged.
• If the sensor circuit is good but E9 remains, the control board is likely defective.