We have an over-the-bath shower with its own Bosch Powerstar AE125
water heater. Recently it has stopped producing hot water through the
bath tap, although there is still hot water if we switch it to shower
only. When we checked the heater, one of the three units in it is not
working . . . at least, it throws the breaker every time. The other
two seem to work just fine.

Any suggestions? Thanks!