Baxi Luna issue

Discussion in 'Boiler Forum' started by mikeplummer, Jun 13, 2013.

  1. mikeplummer

    mikeplummer Plumber

    Messages:
    190
    Location:
    Ontario, Canada
    Hey,

    Baxi Luna 310 Fi combi boiler


    I generally don't get into extensive service on gas appliances.
    Had a customer call with "no hot water at shower" but has very hot water at lav and kitchen sink. I suspected moen cartridge so I replaced it.
    After nosing into it more, there is hot water when using the shower head, but not when using tub spout, unless moentrol valve is open to allow only a small amount of flow then it gets hot.
    this tells me the boiler is not keeping up with the higher flowrate of the tubspout vs showerhead or sink faucets.
    This boiler has been in for a few years I believe and this problem only started after the original installer performed a service on it and changed a diverter inside the boiler that controls the flow for heating/domestic water load.
    There shouldn't be any control required for heat vs domestic flow as there is no call for heat, just to be sure I turned the boiler to only domestic hot water mode and the problem remains, making me suspect its not the diverter itself.
    Any ideas what else could cause this?
  2. Dana

    Dana In the trades

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    3,027
    Location:
    01609
    The thing can deliver 100,000BTU/hr, which is enough for a shower flows, but pretty marginal for tub fill rates. It's possible that the heat exchanger is liming/scaling up if this is a hard-water area, but whatever the service guy hacked inside the boiler is the more likely culprit, and you may not be fully backing out whatever tweaks he made. Did changing modes make ANY difference? (Measure the water temps at the faucet in both modes, running at least 10 gallons in each mode.l)
  3. mikeplummer

    mikeplummer Plumber

    Messages:
    190
    Location:
    Ontario, Canada
    thanks for the quick reply.

    the previous guy simply removed the diverter valve assembly as a whole and replaced it with a new replacement - I wouldn't say he "hacked" anything in.

    secondly changing the mode made no difference at all.

    I got the service manual online and it doesn't show any procedure to adjust the diverter assembly.
  4. Dana

    Dana In the trades

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    Location:
    01609
    If it screwed up the DHW output, intentional or not, it was hacked. Was it really the right part? Was it installed correctly? If the change in performance was concurrent with the swap out, it's a flag. Why was it changed out?
  5. Tom Sawyer

    Tom Sawyer In the Trades

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    Location:
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    I'm betting in a limed up exchanger
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
    New England
    SOme of these things use a flow restrictor to help ensure you can get enough heat rise. If he changed that, allowing more flow, it will never be able to get as big of a delta-T as it did before.
  7. mikeplummer

    mikeplummer Plumber

    Messages:
    190
    Location:
    Ontario, Canada
    As far as I can tell without pulling it back out it looks to be the same assembly as he took out, it appears that everything is where it should be as far as connections to it. he is a local heating contractor that I work with often and is professional in workmanship.
    I do agree that the new problem coinciding with the part swap is not coincidental, but in fact something during the process caused this.
    I was suspecting that the filter in the flow restrictor may need cleaned and that the heat exchanger has likely never been flushed.

    thanks for all the help so far guys
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    On one (long since replaced) boiler I had, they specified various restrictors depending on how the burner was jetted...the external appearance is pretty much the same...it may have been replaced with a larger one. The only way to tell is to look very carefully, and maybe even check part numbers. Some may be marked on the outside. Try this: at an unrestricted faucet (say the WM supply), run the hot out full force and measure the flow rate into a bucket. Compare that to what the boiler says it should have for a flow restrictor. You may need to do this for a few minutes to equalize things between the tempering valve and what may have been stored inside while the boiler comes up to full temperature (not much, but it could skew the results - you want steady state, and that takes a bit of time to achieve).

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