Bosch tankless water heater is giving an error code of C3 - Flow sensor (14) does not detect water recirculation: check pump and connections, check recirculation circuit for any blockage. This water heater is not equipped with a recirculation pump, and does not have a recirculation pump in the system. In the settings changed the recirculation to off and reset rebooted the water heater. The error code has been reset. Installed new Grundfos Alpha Recirculation Pump with crossover tee. Pressurized, removed the air from the lines, and put the system into service.