creosote clogging flue second time in three months

Could be unseasoned wood or choking down for a slow burn a little too much.

If possible re-split into smaller splits and then only burn hot as possible but only using a few splits at a time...after you clean up or remove the chimney cap. Good luck.

In your photo it looks like you are burning a fairly smoky fire, which makes me ask what sort of moisture readings are you getting on the inside of freshly split pieces of wood? Most people agree you should be shooting for 20% or less. As for that top plate, your suspicion is correct that it should be tight to the top of your clay flue tile. When I installed my flex liner I stuffed insulation down my clay flue as far as I could push it (about six feet) all around the flex liner before I mounted and sealed the top plate. The top of your flue above the roof line is going to be the coldest area of the flue and this is the same part of the flue that has the coolest exhaust gas temperatures, which produces creosote. That is why chimney caps are always the first place to clog up with creosote.

If I were you I would pull off the rain cap, connector and top plate after you finish burning this season and put some insulation down your clay tile around your flex liner for at least a few feet. While the top plate is off you can clean that top edge of the clay tile and dry fit the top plate to make sure it sits flat. Then you can run a thick bead of silicone caulk along that clean edge of the clay tile before re-seating the top plate. If you pull up on your flex liner to put some tension on it before you tighten down the top connector it will help pull the top plate down snug to the tile liner for a good seal. Just be careful you don't pull on the flex liner too hard and pull it loose from your stove/insert. If you have a T-connector at your stove you want to check and make sure you haven't pulled it up out of position. If everything looks good down below you're good to go. If it looks like you overcooked things and have caused your T-connector to tilt upward out of position just wait a couple of days until the caulk up top is well cured and then you can go back on the roof and loosen the top connector and release a bit of the tension on the flex liner until you have enough slack to put your bottom T-connector back into its proper position. Good Luck.

First thing I would do is change cap. Second from the looks of your smoke you are burning wet wood. You answered your own problem when you said --I took a picture of the chimney cap and can see it is coated with black. That is from to cool of fire with wet wood. With dry wood I clean my chimney every other year and I get about but a cup of brown powder.

That cap has got to go. Also, the top plate should be sealed down to the clay tile that sticks out of the chimney. Since its off center like that, I'm guessing he didn't stuff the top with ceramic wool insulation. It should be, it not only keeps The liner centered, but it keeps heat from escaping around the liner. That being said, I also assume you don't have a block off plate at the bottom? It's not always necessary, but it never hurts. It definitely needs blocked at the top though!

How high is the chimney?

How seasoned is your firewood?

There are probably multiple factors causing this issue.

Great first post for helping to educate everyone

The picture may not be the best but those look like cedar shingles. Another reason not to slack on your chimney maintenance.

At very least, the top plate should have flanges bent on 90° on all four sides of the clay tie, and should be caulked well between the plate and top of the tile.
Don't look like it meets height requirements either.
Wet wood and smoldering burns is my guess of the build up problem.

It is tough to tell. The top plate is pretty obvious though.
And they look like real cedar shakes, and not in the best shape.

Also see lots of tall trees. That could be working against you to.

Hogwildz said:

At very least, the top plate should have flanges bent on 90° on all four sides of the clay tie, and should be caulked well between the plate and top of the tile.
Don't look like it meets height requirements either.
Wet wood and smoldering burns is my guess of the build up problem.

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Often it's not possible to bend the top plate down over the clay. First, the SS plates we use are to heavy to bend, second, the top plates are the same size as the clay. 13"x13", 18"x18" and so on. Stuffing the top with roxul to center the liner and caulking it down is the most common method.

Answers to all previous questions would be very helpful.

Is it just the cap that is getting clogged? That can be a more common problem and that type of chimney cap already stated can be prone to clogging.

If it is just the cap, it can a simple fix and often means just getting a new one and getting on the roof every 3 months to break off any residual formation.

If the entire liners is getting massive amounts of creosote buildup that does signify a much larger issue at hand. In which case answers to previously asked questions will help significantly.

Thermometers are less than £10 and will give a great guide if you're burning hot enough, I was no where near hot enough initially without a thermo.

webby3650 said:

Often it's not possible to bend the top plate down over the clay. First, the SS plates we use are to heavy to bend, second, the top plates are the same size as the clay. 13"x13", 18"x18" and so on. Stuffing the top with roxul to center the liner and caulking it down is the most common method.

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I know all too well how thick the plating is. I bent mine with 4" hand brakes, and it was a slow process, small bends at a time, small angles at a time. Luckily I have the tools.
Not going to bed it over a 2x4 without butchering it in the process. Does look like he has enough to make bends on that top plate.
I purposely ordered mine large with bending the edges in mind. To just caulk a flat plate over the tile leaves too much room for failure in my opinion. Of course if that is all you have to work with, than ya gotta do what ya gotta do. I don't see why whoever orders it, can measure and figure ahead.

Hogwildz said:

I know all too well how thick the plating is. I bent mine with 4" hand brakes, and it was a slow process, small bends at a time, small angles at a time. Luckily I have the tools.
Not going to bed it over a 2x4 without butchering it in the process. Does look like he has enough to make bends on that top plate.
I purposely ordered mine large with bending the edges in mind. To just caulk a flat plate over the tile leaves too much room for failure in my opinion. Of course if that is all you have to work with, than ya gotta do what ya gotta do. I don't see why whoever orders it, can measure and figure ahead.

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Because we do dozens and dozens of liners a year and stock hundreds of liner components. Standard size plates simplify the whole process and they work just fine, although I would prefer it to be bent over the edges. It's just not possible most of the time.