Bosch 125BNG gas water heater-Luke Warm water

Discussion in 'Tankless Water Heater Forum' started by westp1234, Dec 6, 2011.

  1. westp1234

    westp1234 New Member

    Messages:
    7
    Location:
    texas
    This is my first post so forgive me if I'm in the wrong section. However, the problem I am experiencing is that my WH only provides luke warm water. The system seems to be operating normally. I turn the hot water on the burner ignites ,the flame is blue , but the water is Luke warm . One thing I did notice is that the heat exchanger doesn't get very hot when the system is on. Is that normal? Also , the flames on the burners only gets about a half inch high from the burners.

    Any help will be highly appreciated.
  2. Dana

    Dana In the trades

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    The flame regulator probably isn't functioning right- you should be able to get the thing to ROAR at high flow. IIRC this unit has the same mechanical feedback as a log of older European tankless units have.

    Download the manual, pull of the outer cover, and see what the flame-control slider is working against. Usually it's a cam of some sort working against a spring-loaded (internally) valve/regulator. If the part that should be riding on the cam isn't come up, see if you can't gently tease it free and get it working again. Sometimes there's an adjustable limit-screw that can be tweaked in/out a bit to let it operate in a less sticky region.
  3. westp1234

    westp1234 New Member

    Messages:
    7
    Location:
    texas
    Thanks for the response,I will give it a try.

    BTW....Can you tell me if the heat exchanger is suppose to get hot when the unit is on? Because mines is cold when the heater is on.
  4. Dana

    Dana In the trades

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    The heat exchanger will get hot, but only as hot as the hot water. If your flame isn't modulating up and the water temp is tepid or cold, the heat exchanger will be tepid or cold due to the cooling effect of the water running through it.
  5. westp1234

    westp1234 New Member

    Messages:
    7
    Location:
    texas
    Make senses.... So if that's the case the flames is actually what heats the water up correct? I was under the impression the water was heated as it passes through the heat exchanger. I thinking my problem is that my flame is not modulating up high enough to really heat the water properly. As I mention in my previous email my flame only gets about a half to a full inch high. Is that normal? I tried to upload a picture but I keep receiving an error.

    Thanks
  6. westp1234

    westp1234 New Member

    Messages:
    7
    Location:
    texas
    flame.jpg -picture of my flame.
  7. Dana

    Dana In the trades

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    As I stated before, the flames should really roar (as in much higher than 1/2") at full flow, but should vary with the water flow and temperature adjustment. (If it's set to put out scalding hot water the flames will be higher at a given flow than if its set up to deliver tepid water.)

    The flame front in the picture looks like its stuck at it's minimum modulated fire, or very nearly that. If it's not changing at all between minimum water flow and with the faucet full-on, it's not modulating- it's stuck.
  8. westp1234

    westp1234 New Member

    Messages:
    7
    Location:
    texas
    The slide on the flame regulator appears to be functioning correctly , but the water is still luke warm. Bosh sent me a water valve rebuild kit . I installed it and still no luck. Also , the tank will not come on now unless you turn on two hot water sources. (IE. sink and shower) Do you have any other suggestion to solve my dilemma.

    Thanks again...
  9. Dana

    Dana In the trades

    Messages:
    2,837
    Location:
    01609
    Something is sticking or maladjusted- it shouldn't take excessive flow to start an ignition cycle.

    When you say it's working correctly, are you seeing an increase in flame height?

    These beasties often regulate the output temp when the flame can't keep up by restricting the flow- it's conceivable that the internal mixing valve is sticking or restricted, but I'm thinking that's what the rebuilt kit should have taken care of.

    If you have hard water and it's been in service for more than a year, it's possible that it's liming up on the inside of the heat exchanger. To de-lime it you have to give it a good rinse with white vinegar for an hour or so, which requires un-plumbing it from the water system. A small submersible sump pump in a 5 gallon bucket with 2-3 gallons of white vinegar running for an hour is usually sufficient. Turn off the gas, disconnect the potable plumbing, and plumb the output of the sump pump to the cold side (or hot) of the unit, and a hose hooked to the other side returning to the bucket, letting it run for an hour or so. (In hard-water country installing them with isolating ball valves and hose connections for frequent deliming is usually a good idea.) Don't put in anything stronger than vinegar or you'll likely damage the heat exchanger.
  10. westp1234

    westp1234 New Member

    Messages:
    7
    Location:
    texas
    Turns out it was the water valve that was malfunctioning. I installed a new and it fired right up.

    However, I do want t thank you for all your help with this matter.
  11. westp1234

    westp1234 New Member

    Messages:
    7
    Location:
    texas
    Turns out it was the water valve that was malfunctioning. I installed a new and it fired right up.

    However, I do want t thank you for all your help with this matter.
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