All of the Bosch gas and electric tankless water heaters are tested from the factory before shipping. The Bosch tankless water heaters are pressure tested for functionality, operation and leaks. Bosch always ensures that the Bosch tankless water heaters are 100% reliable and operational when they leave manufacturing.
When Bosch has finished testing the gas & electric tankless heaters they will then place colored caps (red for electric tankless or yellow for the gas tankless) on the water inlet and outlet of the heater to prevent any residual water from damaging the insides of the unit and the box it is packed in.
Please see the image below that shows the caps on the bottom of a gas tankless water heater.