Bosch AE115: Need some debugging help.

Discussion in 'Tankless Water Heater Forum' started by calvin1649, May 1, 2009.

  1. calvin1649

    calvin1649 New Member

    I purchased this heater used, so no warranty. It worked great for about a month but now I am having some intermittent trouble with it.

    When it's malfunctioning, the unit will turn itself on and off about every second or so. The on/off cycle is very steady and seems unaffected by how much water is coming out of the faucet. I can make it stay on by slowly turning the temperature dial down until the light stays on. This, however results in very tepid water, sometimes I have to turn it all the way down. Also keep in mind, I keep the temp dial a little over half way during normal operation so it's not like I'm trying to boil clams while I shower!

    Here's what I've checked.
    1. Hot waterflow at either tub is about 2Gal per min
    2. Impeller/propeller thing-do that senses water flow spins freely and constantly at any hot water flow over a trickle.
    3. Wiring is done to spec and voltage to both circuits checks out (keep in mind this thing worked for a month just fine)

    Has anyone esle fixed a simialr problem?

    I'm thinking it's either a faulty flow sensor ($60) or a faulty control unit board ($250 - Ouch!). Both parts are non-refundable, of course. So I'd like to get some better odds against making a $310 shipping!

    Thanks in advance!
  2. clocker33

    clocker33 New Member

    AE115 debug

    This can eliminate some possibilities:
    Input pressure: 15psi-150psi
    Output Flow: .6gpm - 2.7gpm
    The impeller will spin but no heat will be produced outside these ranges.
    The gpm rate is determined by temperature rise. Measure ground water temperature as it comes into the house; let it run for a minute before you measure.

    GPM/ Rise.
    45 F degree rise will give you 2.6gpm ( 70 heated to 115 F degrees = 2.6gpm)
    50 = 2.3
    60 = 2
    70 = 1.7

    You can't control the incoming temperature but you can control flow at the output valve or faucet.

    If none of this helps, then I would think you have a mechanical problem.
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