The display shows F06; the heater does not respond to thermostat changes.

Safety first: Turn off power to the heater before accessing internal components.

• Locate sensor: Find the Nirvana water temperature sensor (thermistor) threaded into the water manifold or installed in a sensor well.
• Inspect wiring: Check the sensor cable for cuts, abrasion, or rodent damage. Ensure the connector at the main control board is fully seated and free of corrosion.
• Resistance check: Disconnect the sensor and measure its resistance with a multimeter. Compare the reading to the Nirvana temperature/resistance chart (e.g., around 10kΩ at 77°F/25°C). If the reading is open, shorted, or far off spec, replace the sensor.
• Check placement: Make sure the sensor is fully inserted into the water stream and not exposed to air pockets.
• Replace if needed: Install a new OEM Nirvana thermistor, using thread sealant if threaded. Reconnect wiring, restore power, and test operation.