If anyone has seen the following mystery problem in a natural gas water
tankless heater before and knows the fix, I'd be grateful to hear it.
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
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