Heater outer casing feels unusually hot to the touch.

Safety: Turn off power and allow the unit to cool. Risk of burns.

Steps:

• Check for leaks: Inspect for water leaks that may have soaked the internal insulation.
• Measure water temperature: Verify that water is not overheating (above setpoint). If it is, test and replace the thermostat or NTC sensor.
• Environment: Ensure the heater is not installed in a confined, unventilated space with other heat sources.
• Insulation damage: If insulation is wet or degraded, the heater's efficiency and safety are compromised; replacement of the unit is usually required.