When cold water is run, the unit's exhaust fan goes on briefly after the cold water stops. This fan is supposed to run a few seconds after the hot water is turned off to exhaust gases from the burner unit. The fan is not supposed to run when cold water alone is run.
A Bosch-recommended plumber installed the unit. Bosch told the installer it had not heard of this problem before.
The installer added a "water hammer arrester" on the cold pipe leading into the unit. This did not fix the problem.
Bosch has offered to send out a new water heater. We are trying to avoid this costly step as we don't know if it is defective. It heats water just fine.
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