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!
Even stranger is the fact that you think the tap is a problem when the water heater trips a breaker.
Whether the tap is a potential suspect depends on what kind of tap the bath tub has. If it's seperate valves for the hot and cold, then no it sure isn't the tap. If it's some kind of combined valve, tempering, etc, then yes it's possible it's the valve. But, per Ed's comments, clearly you have a problem with the water heater, since it's kicking out the breaker. I would start there. Also, you can verify if water from the water heater is coming into the tub by simply shutting off the valve on the water heater when the bath is on hot and running.
The only thing I can think of that might explain what you are seeing is this. The heater has multiple elements. It uses only some of them for low demand, eg the shower. When it goes to use all of them for the tub and finds something unusual, eg the breaker is tripped and no power to one element, maybe it shuts down completely.
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