Weird back puff from my Princess

[spudman99]

OK team, this is a really wierd one that I can use some help on.

On Saturday, I was standing next to my Princess Insert (PI29). This was about 3 hours into a medium burn, added 3 oak logs on hot coals. Got them charred, closed the bypass, set and forget. So the wood was burning just fine, fan on full speed, thermostat set at about 2pm cause it was cold. Cat well into the active zone, STT was about 200deg (all normal).

I then hear a "clunk" and look over and see a back puff of white smoke coming out of the bypass handle opening. Never heard or saw this in any other thread. I then open the bypass, turn down the thermostat and wait. Puff was only the 1 time but the room stunk. I let the fire then go out as I had no idea what the clunk was. With fireplace now cold, I took off the side panels. Bypass lever and wires are fine. Checked the bypass and it lays flat, ran my hand around and there was no debris. Oh and I was sure the bypass was in the fully closed position (hopefully my old age is correct on that). Today I ran my camera up the liner and it is set tight to the unit.

Two questions:

Are there any possible moving or loose parts that could cause a back puff?
Or did I not have the bypass fully closed (even though I thought I did -- senior moment) and that clunk was it fully seating resulting in the back puff?

Why would smoke puff back out the bypass handle as I thought that chamber was isolated from the firebox. Somehow smoke was in that area. I just dont know.

What say you the wise and knowledgeable BK community.

 

[stoveliker]

That chamber is not isolated from the firebox - at least in freestanding stoves where it is the "after cat pathway" for the exhaust.
With a locked bypass, if I would get a backpuff, I think there's a decent chance I'd get some smoke where the bypass handle goes in. No seal there afaik, just a tight fit of rod and hole.

 

[Dieselhead]

I’ve had that happen a few times, most cat stoves are susceptible to it. The cat is working great, upper active range the wood is off gassing quicker than the cat can process it and it ignites the smoke in the firebox. The exhaust area can’t handle the volume completely and the stove burps a little smoke from wherever it can. Even the intake side.

 

[stoveliker]

Hasn't happened here. Maybe my draft is a bit higher tho

 

[Tron]

I then hear a "clunk" and look over and see a back puff of white smoke coming out of the bypass handle opening.

I agree with @Dieselhead, that's especially likely if the wood was just smoldering. If you had active flames, not so much.

 

[Highbeam]

It happens. Called backpuffing or whoofing. I just had one about a month ago that shot white smoke out of the flue collar which would be downstream of the cat.

Why would you load 3 more splits into a firebox at full boogy three hours into the burn? That fresh fuel woud then be offgassing into a hot system with a closed thermostat until it ignited with a flash. These things burn best in cycles. Fully load it each time if you can. Sometimes you just need a little more to top it off before bed though so if you must then consider measures to reduce backpuffing.

 

[spudman99]

Thanks for the replies. With regard to Highbeam, I loaded 3 splits on plenty of hot coals and some charred wood, to get me thru the day and until nightly reload. Solar heating means I can slow burn. The backpuff happened on a mature load after I heard a clunk, looked over and a sizeable puff. Sound was more like aluminum clinking and not cast iron. I have an inline damper above my insert and I though the baffle fell down creating a blockage. Boroscope showed the damper working just fine, I have no idea where that noise came from.

But thanks to all. I started it up this morning with a small load to see if there were any new problems. None, so I am now starting a full load and hopefully this was just a one off.