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Thread: On Demand heater problem

  1. #1

    Default On Demand heater problem

    Help!! We have a Bosch Aquastar 125-B on demand heater that was installed 3-4 years ago. We have a Price-Phister 2 handle bathtub faucet.

    During showers all of a sudden the water goes to cold only. To get hot water back you have to turn the cold water off and wait several seconds. This can happen once per shower or multiple times.

    Where do I start troubleshooting? I have the control dial set to the 1/2 gallon per minute start-up and the temperature setting all the way up. Do you think I need to turn the temperature down some (Their website says in FAQ's that mixing too much cold water to temper the water can cause the unit to shut down due to low flow, however I think that this applies to single handle mixers and don't know about 2 handle faucets)?

    This is not a new problem, wife says has been going on for a long time (not sure if has always been this way). Any help or suggestions would be greatly appreciated.

    Russell

  2. #2
    DIY scratch-pad engineer leejosepho's Avatar
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    Default

    Quote Originally Posted by ophnurse View Post
    Where do I start troubleshooting? I have the control dial set to the 1/2 gallon per minute start-up and the temperature setting all the way up. Do you think I need to turn the temperature down some (Their website says in FAQ's that mixing too much cold water to temper the water can cause the unit to shut down due to low flow, however I think that this applies to single handle mixers and don't know about 2 handle faucets)?
    That would be my guess: Turn it down a bit. Either from a restrictive buildup inside or from the cold-water mix-in ratio being too high, it sounds like the unit is overheating and shutting down for safety.

  3. #3

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    Thanks, I'll give it a try and see what happens.

  4. #4
    Master Plumber Redwood's Avatar
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    Set the temperature to about what the temperature is that you like showers then try it so you are using almost all or, all hot and see what happens.

    I alomost guarantee it is flow related.

  5. #5
    Moderator valveman's Avatar
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    Is this working off a well pump or city water pressure?

  6. #6

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    City pressure. I have turned the temp down and we are trying this for a while.

  7. #7
    DIY Member TheOak's Avatar
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    On a potentially related note ...

    When last have you checked the inbound filter?

    When last have you flushed the unit?

    It might be due for a check ...

  8. #8
    Master Plumber Redwood's Avatar
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    That would be a great idea!

  9. #9

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    Measure the temperature of the hot water run alone at the bathroom or kitchen sink.

    Do you have a tempering valve installed at the water heater?

  10. #10
    DIY Member TheOak's Avatar
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    Don't some shower heads have anti-scalding "stuff" in them? Perhaps the shower head is malfunctioning "thinking" that the water is too hot and blocking the hot completely?

    Have you tried another shower head?

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