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

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Bosch PowerStar125 won't heat and I can't get one element to work

My Bosch AE125 has been working well for over a year then the other night it suddenly stopped. I went through the troubleshooting section of the guide and determined that one of the thermal cut-outs on top of the first of the three elements (one to far right facing them) would not reset. The light does not come on and I have no hot water. The transducer spins and there is no blockage in the inlet filter. The buttons in the thermal cut-outs atop the other two elements will reset and when I put the power back on the other two elements heat the water but the light does not come on and the first element does not work and the button on the thermal cut-out won't reset. I ordered a couple new thermal cut-outs and replaced the one that appeared to be bad but that has not changed anything and the problem persists with the exact same symptoms. Also, the new thermal cut-outs do not seem to reset like the ones do on the two elemets that work. The new thermal cut-out behaves just like the old one did and the button doesn't click and reset like the others do. Additionally even though I will get some hot water (even though the indicator light doesn't come on) when I first reset the cut-outs once I turn the water off they pop and I get no hot water at all unless I reset them again (only the middle and left thermal cut-outs will reset). Please help it is not fun heating water on the stove to wash myself and all the dishes every day.

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  • yurya2 Jan 20, 2009

    Thanks for the answer. I believe you are correct. I did get a hold of Bosch and they told me the same thing. I have checked all the wires and connections and everything else is good. However, I don't have a multimeter and need to get one. Also, if it turns out that the copper canister unit is bad, what then? I need to do the Ohm out check but through a process of elimination that is likely the only thing left to be wrong. If the one element is bad does that mean the whole thing will have to be replaced? Or, is there a fix for that?



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It sounds like you have a copper canister unit. Ohm out the elements in that one canister. the directions are on the websight for bosch, or I can walk you through it. But you will need a digital multimeter to do this. If you have a blown element in that one canister, then the tco will not reset.

Posted on Jan 19, 2009

  • Tim Hamlin Jan 20, 2009

    Yes unfortunatley the heater was designed by controled energy. They make the heater. If you are the original purchaser it would be under warranty and bosch will send you a new heater. if your serial number begins with or before #62 then they dont want the old one back they will just send you a new heater. You will have to install it, or have a electrical tech or plumber install it for you.

    But the only way they will take care of this for you is to get the ohm readings on the elements. Then they will determin the unit is no good, and send you a new heater.


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Hi did you ever get this resolved? I'm going through the same thing and looking for some advise. Thank you.

Posted on Dec 27, 2010


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