Harman Absolute 63 whomp, whoop, flicker, or flutter

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Burn pot was replaced with no change, currently working to move it near a door to vent it straight out the door with minimal piping. I did notice the appliance adapter to tee didn't seal super well so that could have been part of the problem. Issue persists, though not as bad, with stove vented straight out door.
 
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Okay, to wrap up the saga, the dealer installed a new stove, all piping, and did a quick test burn, like as much as you can do in 85 degree weather. There is nothing out of the ordinary at this point but the proof will be in the pudding when winter returns.

While I'm not thrilled it took this long I'm happy to be on the other side. Thanks all!
 
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Long Road lets hope for a good outcome
 
From what I've seen, the strobe flame and thumping/whomping sound is something that has been happening with some Harman stoves for many years. I don't think an actual cause and solution has ever been found. I absolutely love my Harman P43, but it gets it occasionally also. My P43 is my 3rd brand of stove over many years and it's by far the best and wouldn't want a different one.

Luckily for me, mine is mostly the strobe effect with little to no whomping sound.
When mine does the strobe thing, I can put my hand on the hopper lid and feel it fluttering. Or if I release the hopper latch and crack the lid open, I can actually feel the lid pulsing up and down. Scraping the burn pot stops it temporarily.

From what I've seen in discussions over the years, it almost seems like some sort of resonance between the air intake and exhaust. It appears to be like a similar effect in cars when one window is opened called buffeting which is also known as Helmholtz Resonance.

I'd love to find a lasting solution, but there have been many discussions and it often comes back after solutions that seem to work for a while. Why it only seems to effect a percentage of Harmans is also a mystery.

Here's a few old discussions using the search term "Harman Strobe Flame" Many of the discussions are for older Harmans that had a different burn pot/air configuration, but it shows it's been going on with some for a long time.

Ray
 
Also to add:
When I mentioned the hopper lid, I also noticed that in my case, the thumping/whomping sound seems to happen when during the feed cycle when the sliding pellet feed plate is open. I'm also pretty sure that when the flame is strobing, if I open the hopper lid, the strobing stops. This fits with the resonating theory like a moving car, because when it happens in a car, opening a second window often stops it.

Ray
 
My P61a has done the flicker/strobe flame, but it seems to only do it with certain pellets. I generally run Somersets and it doesn't do it with them. Or at least I haven't noticed it.
 
Well, I'm back! And not just because I just wanted to say hi either.

The second stove does the same thing albeit, much less. I've tracked down the problem to the seal on the clean-out tee.

My theory is that the foam seal let's by just enough air to act like a drum head. Currently I'm waiting for the shmoo I pumped into the clean-out cover to dry to test my theory.

This is a brand new tee and as I was tracking down some smoke leakage, which was from everywhere, I noticed a jet coming out of the cover. Hopefully this puts any leakage to bed AND resolves the issue. If I was the dealer I'd be pretty perturbed having sunk so much time into 3 bad tees, but nothing definitive just yet.

Thanks @Ocelot that is all helpful information.
 
Oh no kidding, you calls always cut a silicone seal the thickness you think it moves and set it in the cap…just a thought