"shim ring" for secondary air flap?

[Megunticook]

Stove's getting a bit too much air even when I close the primary air control completely, am going through a process of elimination to find the culprit. Last night I had 3 small hardwood splits on a modest bed of coals with the damper closed and primary fully shut and I wasn't able to extinguish visible flame like I normally can. I ran it fully closed down for a good hour or so, cat only peaked briefly at 1600 but stovetop thermometer ended up pegged at 900 for 30 minutes or so. Not ideal and not normal for my setup.

Right now I'm taking a hard look at the secondary air control mechanism to make sure it's closing completely when things heat up.

Playing with it a bit on the cold stove it seemed like it might be sticking open even after I manually moved the thermostat tab to relieve any tension on the control lever attached to the flap.

I had vaccuumed this area earlier in the fall but decided to disassemble and inspect more closely.

Fair bit of fine caked on dust on the flap and around the opening in the stove back, so removed all that with a damp rag. Then checked the VC factory service manual just to make sure I wasn't overlooking anything.

The manual says "Secure the secondary air flap to the stove back with a similar bolt and a shim ring. Tighten the bolt holding the air flap until it is snug, then back it off 1/4 turn. Ensure the flap moves freely up and down and that the flap rests at or near the closed position."

I had nothing but a small screw holding the flap to the stove. Is a "shim ring" just a thin flat metal washer? I guess I can find something to work. Does this go between the flap and the stove? Or between the screwhead and flap?

Does the position of the flap in this picture look correct for a cold stove?



Tonight I'll do another burn and watch the operation closely.

I've replaced the secondary air probe at least once, I think twice maybe but I forgot to make a note the last time. The probe itself still looks OK to my eye, but I'm ordering a spare to have on hand anyway.

Next I'll probably make sure the primary flap is closing all the way. It's a little bit of a pain since I have an OAK installed but I might be able to just drop that and the duct down without having to reposition the stove.

Just for kicks I took a peek at the stove bottom to see if I could identify those "EPA holes" everyone references. I don't see them...where are they exactly? I thought the Encore 2550 had those but not I'm not sure sure...

 

[Eman85]

Your stove is newer than mine but yes the flap look correct, just slightly open cold. I moved mine through it's range and found it would hang, the rod would bind on the flap. I just filed the edge a little and it was smooth after that. Pay attention when the stove gets real hot. Mine will actually open back up as the spring keeps expanding. I could never get a definite answer from anyone as the the actual function of the secondary air. It almost seems to me it's designed to open and cool the cat past a certain temperature.
Flames with the air control shut sounds more like a leaky gasket. Check the ash pan and all of the door gasket for any signs of leakage. Can also leak around the glass.

 

[Megunticook]

Your stove is newer than mine but yes the flap look correct, just slightly open cold. I moved mine through it's range and found it would hang, the rod would bind on the flap. I just filed the edge a little and it was smooth after that. Pay attention when the stove gets real hot. Mine will actually open back up as the spring keeps expanding. I could never get a definite answer from anyone as the the actual function of the secondary air. It almost seems to me it's designed to open and cool the cat past a certain temperature.
Flames with the air control shut sounds more like a leaky gasket. Check the ash pan and all of the door gasket for any signs of leakage. Can also leak around the glass.

Hmmm, had no idea the secondary air would "open back up"--that seems counterintuitive to me but maybe the VC engineers had some idea along the lines of what you say. Seems like it would make for a hotter fire though.

I checked all gaskets thoroughly with pieces of paper when I was prepping for the season. I changed the ask pan gasket and the glass gasket just for good measure but the rest all seems to be sealing well.

I suspect I do have some leakage where the top meets one of the sides, last season while starting a fire during an extremely low-pressure day, I saw a little smoke come out from one of the seams. I caulked it with gasket cement this fall as a temporary measure but it's probably time to rebuild the whole stove.

 

[Megunticook]

p.s. I just saw an online review of the secondary air probe that controls the flap--customer described exactly what you said happened on your stove, where the flap first closed and then opened as the stove got hotter. Apparently the thermostat coil will just continue expanding, which pushes the tab with the control lever attached to it up to the 8 or 9 o-clock position. This customer said he spoke with VC about this and they told him it's not supposed to do that. Hmmm. That seems like a serious issue. In any case I wonder if that's what's happening to me? Will try and heat the stove up tonight and see.

And now I see where this was discussed here a couple years ago: https://www.hearth.com/talk/threads/secondary-air-probe-opens-back-up.194481/

Sounds like poor engineering and/or poor quality control on the replacement parts. Boy, that seems pretty irresponsible to not come up with a fix on this and continue selling these questionable parts.

 

[begreen]

How tall is the flue system on the stove?

 

[Megunticook]

About 27 feet. 8 inch connector with one elbow into thimble then straight up 8" clay tile flue of interior chimney. Strong draft but until recently I was always able to knock down flames if needed using primary air control.

 

[begreen]

27' is a tall flue. Have there been any changes in or around the house that might have strengthened draft? This could be better sealing and windows, changes in home ventilation, or even tree removal outside.

 

[Megunticook]

No changes.

Will run some tests tonight. Where exactly are those "EPA holes" in the bottom?

Also, where does the secondary air inlet route the incoming air? Does it end up below the grill somewhere?

 

[Megunticook]

After some tests last night I don't think the secondary air inlet is the issue.

Watched it closely as I started up a fire, warmed up the stove, and engaged the catalyst. Secondary air flap seemed to behave correctly. I didn't get things super hot but the catalyst was up to 1400 at one point (750 stovetop) and the flap stayed shut once the stove warmed up.

Even when the flap was fully shut, it was still impossible to knock down the flames by closing the primary air shutter completely. So I don't think the secondary air is really the issue.

I've removed the OAK, vaccumed up any dust around the inlet, and worked the primary air control lever back and forth. It seems to be operating properly and appears to close but maybe there's a small gap when it's in the closed position?

Still can't seem to find those "EPA holes" in the bottom. Does the 2550 have them? Where in the heck are they?

 

[begreen]

Has the bypass been checked to make sure it is closing and sealing properly? If all checks out in order then it might be worth adding a key damper to the stove pipe.

 

[Megunticook]

Has the bypass been checked to make sure it is closing and sealing properly? If all checks out in order then it might be worth adding a key damper to the stove pipe.

Yes, used a slip of paper to check all around the damper gasket.

I'm sure key a damper would help as a last resort but this setup ran beautifully for two decades so if I can just identify where the air leak is coming from it should be solveable.

I spoke with our local VC dealer this morning trying to locate a replacement gasket for the primary air inlet, and in the course of conversing he mentioned that he likes to keep the ash pan filled up with ash, in fact he even says he likes seeing a bed of ashes over the top of the grate. Seems odd to me but he thought all the VC stoves run better this way and that it would also help make the fire more controllable by reducing the amount of air feeding the fire from below the grate. What's your opinion on this? Normally I empty the ash pan whenever it fills up.

By the way, I found the "shim ring" for the secondary air flap screw when I removed the outside air duct--it had apparently fallen into the duct receptacle box at some point. I think this helps to reduce the "slop" in the secondary air flap screw/pivot hole, as the screw diameter is quite a bit smaller than the hole in the flap.



Here's a short video of the firebox after stove was warmed up, cat engaged, and primary air control fully closed. This is just 3 small splits of hardwood (well-seasoned). Normally if I close down primary air completely when the damper is shut you see very little flame:

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[begreen]

I found our Jotul F400 ran a lot better with the ashpan full up to the grate. Sealing the ashpan door seems to be more of a challenge than it is for the main stove door.

 

[Megunticook]

I found our Jotul F400 ran a lot better with the ashpan full up to the grate. Sealing the ashpan door seems to be more of a challenge than it is for the main stove door.

Interesting. I'll give it a try. I did check the VC manual and it specifically says "you should remove ash before it reaches the top of the ash pan." I wonder if the idea here is to maintain a healthy flow of air coming from below the grate. So it my case it might be advantageous to cut down on that airflow a bit.

 

[Megunticook]

While observing the secondary air flap in action I notice now that it doesn't close all the way--and after playing with it more I think it's actually designed that way. There's a little "peg" on the inside face of the flap, down near the bottom edge and maybe an inch from the corner, and this peg seems to prevent the flap from fully closing. So even when the stove heats up there's a small air gap. Odd.

So the secondary air inlet is partially open when cold and only closes slightly when warm. Can't really understand what the intention is for that.

No overfiring as I test but been using just a few smaller pieces. Still can't extinguish the flames in the firebox with the primary air control, which makes me uneasy. Would not be comfortable filling up the firebox up right now.

I