Navien exhaust vent screen blowing off - explosion in vent pipe?

Discussion in 'Tankless Water Heater Forum' started by DaveE, Aug 16, 2019.

  1. DaveE

    DaveE New Member

    Joined:
    Aug 16, 2019
    Location:
    Anchorage
    A few days ago, we found our 2009 Navien NR-240A exhaust vent bird screen on the ground about 12 feet away from the end of the vent. Very odd, and has never happened before. I can't believe some neighbor kid is messing with us and it's hard to remove so I doubt birds or other animals are the cause.

    (See update post below - it happened again, this time while my wife was in the backyard...)

    The vent pipe is nominally horizontal and about three feet above ground. The screen had been originally installed with silicone sealant and it was a tight fit to put it back in.

    This a.m., it was on the ground in about the same location.

    Since the screen is mostly open area, it would take considerable internal pressure for it to "blow" out, and we have not heard any explosions. I suppose it could happen in the a.m. when the internal re-circ starts and we are still asleep.

    The unit seems to be operating ok. It was serviced recently (warranty heat exchanger replacement) and immediately after the replacement we got a "flame loss" error code 12. On callback, the tech said the "low fire was really low" and he adjusted it so "both high and low are within spec, at the richer end of the range."

    I'm thinking of installing a webcam to monitor it.

    Anyone ever hear of vent screens blowing off? How likely is there to be an explosion in the vent pipe that doesn't cause significant destruction?!
     
    Last edited: Aug 18, 2019
  2. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    What type of wild animals walk the neighborhoods in Anchorage, AK?
     
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  4. DaveE

    DaveE New Member

    Joined:
    Aug 16, 2019
    Location:
    Anchorage
    Moose (frequently) and bears (infrequently).

    It happened again yesterday while my wife was in the backyard. She heard a pop/thud and found the screen about 15 feet away from the vent pipe. So, it's definitely caused by an explosion in the combustion chamber/vent pipe.

    Delayed ignition is probably the cause, but I'm not sure what to do about it. I will call the contractor back, again.
     
    Last edited: Aug 18, 2019
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