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

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DaveE

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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?!
 
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DaveE

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What type of wild animals walk the neighborhoods in Anchorage, AK?
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.
 
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Joshua Wynn

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Hi did you ever find the cause for this? My unit started doing this yesterday and the water starts off warm then cold then warm, etc. Also noticed a strong smell of propane and my gas meter went crazy when I opened the unit while it was calling for hot water.
 

Eddolproject

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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.
 

Eddolproject

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Same thing happened to mine. It was caused due to the poor air circulation of the unit.
We installed outside in a corner where the exhaust and intake were mixing, creating some sort of combustion. The plumbers installed a pipe to re-direct the exhaust.
Working well
 

WorthFlorida

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Same thing happened to mine. It was caused due to the poor air circulation of the unit.
We installed outside in a corner where the exhaust and intake were mixing, creating some sort of combustion. The plumbers installed a pipe to re-direct the exhaust.
Working well
Thank you on your post.
I suspect the exhaust gets sucked into the intake creating a rich mixture and on ignition, boom.
 

DIYorBust

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I had an issue with a navien causing an explosion in the fire box which blew out one of the connections in the exhaust line. The culprit was the insulation on the ignition wires had failed causing a short arc to occur. The ignition spark occured mostly outside the firebox, and the spark inside was too weak to ignite the gas until a lot had built up. The tech fixed the problem and said he would report the issue to Navien. I would definitely get this looked at.
 
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