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I have a Bosch WR400-1 Tankless Water Heater. The unit is approx. 8 years old. Problem: When the heater is in the on position and hot water is off, the flames stay on and does not return to pilot mode. Your assistance is appreciated.

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  • ikaika_59 Jan 04, 2011


    I pulled both wires one at a time, and both times the flame went out. Please advise on further troubleshooting...Aloha

  • ikaika_59 Jan 04, 2011

    Will check the sensor

  • ikaika_59 Jan 08, 2011

    FYI-I removed the water valve assembly, cleaned inside and out. The plunger was a little sticky, and there was debris in the lower valve. Also checked the plunger on the lower gas valve, it was stuck, and after some pushing and pulling with a longnose plier it moved freely. Replaced the water valve, and the heater worked fine, My heater does not have a water flow sensor. Thanks for your assistance.

  • ikaika_59 Jan 08, 2011

    Not fully



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This sounds like a gas valve sticking....try to pull one of the wires from the gas valve and see what happens to check it out...if it stays on there that confrims it...

If the gas valve is bad and whith the age of the heater you may want to look into a new one...


Posted on Jan 04, 2011

  • D. Floyd Kolb
    D. Floyd Kolb Jan 04, 2011

    Okay then something else is holding on the power to the gas valve... the problem is not that....

    If that is the case the next logical thing would be the water flo sensor...

    I would replace that or have it replaced... it must be stuck in the "on" position....they do fail in the on position sometimes...


  • D. Floyd Kolb
    D. Floyd Kolb Jan 04, 2011

    I think that the sensor should close when the water is flowing and then open when it can check that with an OHM meter...



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