Open following link for Bosch tankless troubleshooting resources,
including Bosch contact information, typical manuals, error codes, tech
support, parts, fuel-saver calculator, service bulletins, water heater
forum, fixya links, disclaimers, and links for finding service
Read manual cover to cover, make sure tankless receives yearly maintenance as outline in manual.
Add a comment with your experience so others with same-similar problem can benefit.
Also take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.