Bosch 250 SX NG - Very Slow to Heat Water

Discussion in 'Tankless Water Heater Forum' started by Dmmoroney, Mar 31, 2019.

  1. Dmmoroney

    Dmmoroney New Member

    Joined:
    Mar 31, 2019
    Location:
    NY
    Hello All,

    As you can see from the headline, my Bosch 250 SX NG takes a very long time to provide hot water. I have a shower & sink in the bathroom, and a sink in the kitchen. At all locations the water will get hot, but it can take minutes sometimes. The kitchen takes longest, and happens to be the longest run at about 50 ft or so. The bathroom lines are around 15-20 ft. The shower does get hot quickest, and I believe it is the first run.

    Has anyone experienced this? Can anyone shed some light on the issue? Again, it's not that I'm not getting hot water, it's just taking a long time.

    Thank you in advance!
     

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    Last edited: Apr 1, 2019
  2. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    The ignition delay on some tankless water heaters is pretty long, and at low flow it can sometimes even fail to fire right away. Once lit the flow can run slower, but if you're just opening up the kitchen tap to a modest flow it may take awhile to fire, since it can be too close to the flow threshold where it won't fire up at all.

    Try opening up the kitchen tap to full-flow/max-hot and see if it gets there any faster.
     
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  4. Dmmoroney

    Dmmoroney New Member

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    Mar 31, 2019
    Location:
    NY
    Thank you for the reply! So we actually open it all the way when we want hot water, and then we just wait. Sometimes it can take 3-4 minutes, fully open.
     
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Retired Systems engineer for defense industry.
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    New England
    The flow sensor may be defective.
     
  6. Dmmoroney

    Dmmoroney New Member

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    Mar 31, 2019
    Location:
    NY
    Thanks for the suggestion! I'll look into the flow sensor.
     
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    If you haven't done an acid flush on the thing, that by itself may resolve your problem after it is done. One big difference between a tank and a tankless system is the amount of maintenance required. Unless you have very soft water, the insides of the tankless WILL start to get clogged up with minerals. If you don't have the valves installed to make circulating the acid solution through the unit to dissolve those, that will need to be added. Once you have the right setup, the actual process isn't all that hard. Most recommend that be done at least once a year, more if the water is very hard (there are limits set by the unit's manufacturer), or less often if it is very soft. If done annually, it probably takes a couple of hours. IF it hasn't been done, it may take longer. Mineral buildup can clog things up, slow the flow, lower the heat transfer efficiency, and mess with sensors.

    Failing to do that can make a tankless system inoperable.
     
  8. Dmmoroney

    Dmmoroney New Member

    Joined:
    Mar 31, 2019
    Location:
    NY
    Thank you for the reply! I was able to find a YouTube video on how to flush the system. I'll give it a shot. Thanks again!
     
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