Re: Busted tankless electric water heater control board

Wow! Thanks, everyone, for all the replies!

@sam_sam_sam, is there a way to test the optocouplers without connecting the AC lines? I'm a total novice and squeamish working around all that juice. (The water heater is on three 40 amp breakers.)

@CapLeaker, when the board is dead, it's not completely dead. The heater fails to raise the water temperature, but the LED on the unit blinks on and off when water passes through the flow sensor (somewhat randomly, it seems). The full troubleshooting guide...

Hi. I have an old Bosch/Powerstar AE125 water heater in my cabin whose control board died for the nth time. This time around, I figured I'd try to diagnose and repair it. At the end of the board's life its power indicator LED will quickly cycle on and off as water passes through the heater, rather than remaining steadily on as it normally would, and water at the tap remains cold. Slightly increasing pressure in the system by closing the outlet valve seems to delay the inevitable for a little while.

Here's all the info I found from Bosch regarding troubleshooting the board:
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Re: Dell U3011 no display after a few minutes



I signed up to say thanks for this tip! It worked for me, too.

Here's a shot of my joints before I re-soldered them:

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