Heater shows E06 and does not respond to heat commands

Safety: Turn off power to the heater before accessing the control compartment.

• Locate the inlet sensor: Find the Inlet Water Temperature Sensor (Thermistor) threaded into the inlet header or mounted in a sensor well.
• Inspect wiring: Follow the sensor leads back to the main control board. Look for cuts, rodent damage, or corrosion at the plug. Clean any green/white corrosion with electrical contact cleaner and a small brush.
• Check resistance: Disconnect the sensor and measure its resistance with a multimeter. Compare to the SunHeater temperature/resistance chart (commonly around 10kΩ at 77°F/25°C). If the reading is open, shorted, or far off spec, replace the sensor.
• Check for moisture: If the sensor is in a well, remove it and check for water intrusion or rust. Dry the well and reseal with appropriate thread sealant when installing the new sensor.
• Reset control: Reconnect everything, restore power, and clear the error by cycling power. If E06 persists with a known-good sensor, the main control board may be defective.