The following steps have to be performed by a qualified person as you may be exposed to electrical hazards and/or damage the product. Make sure the power supply is disconnected if required and the water supply is disconnected if required.
For the following steps you will need the following tools: Multimeter, Screw driver.
Cut the power supply of the water heater at the main electrical panel and disconnect the battery.
Dismount the heating module cover, the control board cover, the upper element cover and the heating element cover.