Question about Bosch PowerStar AE125 AE125 Whole House Electric Tankless Water Heater...

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Bosch AE125 no hot water, blinking light

Anytime I turn on the hot water, the lights in the house dim slightly, which tells me that the (electric) water heater is on. hat happens now is that the lights flicker several times a second, but the water never warms. I checked the water heater, and the light on the front flashes on intermittently. To clarify, it is off for 0.9 seconds and on for 0.1 second. These are rough estimates but give you an idea of the frequency. I hate this stupid unreliable water heater (already replaced once, only 6 months old), but I cannot afford to replace with something new at this time.

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  • Andy Hutchison Dec 14, 2013

    I should add that I am running the hot water at full blast--probably 3+ gpm. Inlet water temp under 50 degrees F, no breakers tripped, thermal cutouts not tripped, no leaks, filter not clogged.

  • Rocky Vincent Dec 15, 2013

    Sorry about the redundancy. I missed the part where you said the cut outs were not tripped. Sorry. Hope I gave you enough to work with. Rocky



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Hey Andy. Do you have your owners manual? There should be a section near the back that will break down the diagnostic code the flashing light is giving you. If not remove the front cover and look inside should be a wiring diagram and light legend.

Posted on Dec 14, 2013

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  • Andy Hutchison Dec 14, 2013

    The manual says nothing about a blinking or flashing light--only on or off. That's why I came here to see if anyone knew about this unusual situation.

  • Rocky Vincent Dec 14, 2013

    Ok let me do a little research on that model. I'm not familiar with that one. They are in a way all the same. It has a flow meter or sensor to let the control know water is flowing and needs to be heated. Give me a few minutes.

  • Andy Hutchison Dec 14, 2013

    I tried something, and it worked. I ran the water on full hot, 75% flow (lights flickering), and turned down the thermostat on the heater until the light was on steady. I then slowly turned up the thermo to see when it started blinking, and it never did. I turned it all the way to 10 and it remained steady.

  • Rocky Vincent Dec 14, 2013

    Hey Andy. From what I've read there are several somewhat easy checks you can make.

  • Rocky Vincent Dec 14, 2013

    When you said your house lights are flickering it would lead me to believe that the heater is recognizing water flow, and trying to turn on the heating elements. If you have a restriction of water flow the out going temp will turn the elements (heater) off. Check the inlet screen for any debris or mineral build up.

  • Rocky Vincent Dec 14, 2013

    The second thing to check is the reset switch. There is supposed to be one for each element. Turn off the power to the heater and take the cover off of it. There should be a reset button on top of each heater module. Reset each. Also at this time make sure all grounds are connected and tight.

  • Rocky Vincent Dec 14, 2013

    When you cut the power to the unit it should reset the control PCB automatically. Look to see if there is a reset button on the control module. If not then turn the temperature all the way down. Then purge all the air out and by opening a hot water valve like a tub. let it run till no air.

  • Rocky Vincent Dec 14, 2013

    Start off with the temp down on lowest setting. Re-energize the unit. Open a hot water valve and see if it will work at the lowest temp. If so then gradually move it up to desired temp. If there is no change then it would probably be the output temp probe or the control PCB.



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  • 3 Answers

SOURCE: heater is ae125 is about

Hey did you ever get this fixed mine is almost the exact same thing we've been using ours for about 3 years and today nothing. Thanks for your help.

Posted on Dec 25, 2010


  • 1 Answer

SOURCE: our second unit just failed and needs a new controller more money

I have a rinnai infinity 24. Been perfect for 2 years but now only heats water to shower and sometimes kitchen sink.Nothing to bath or handbasin

Posted on Aug 21, 2011

Gene Haynes

  • 5391 Answers

SOURCE: I have a Bosch GWH 425 HNO propane Tankless Water Heater which began intermittently exploding when demand for hot water occurs.

Call a qualified service tech immediately.
Gas explosion indicates dirty combustion parts, and gas is not fully igniting when tankless turns on the gas. So gas builds up and then explodes causing serious damage to tankless, and serious risk to homeowner.

If you need further help, I’m available over the phone at

Posted on Aug 15, 2012

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