As of 2015, there are 17 different error codes for a Bosch tankless water heater. The specific number of codes may vary depending on what Bosch machine is used.
An error code found on the digital interface of a Bosch machine lets the owner know what particular problem is occurring internally so he can easily troubleshoot and fix the problem. For example, a code A3 indicates that a jumper connection is incorrect. The solution is to check and make sure that the connection is correct. This can be seen by checking the upper right hand corner of the heat exchanger.