Failed catalytic combuster and over fire theory...

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oldAGE

Member
Jan 14, 2008
107
South Central WI
OK guys (and gals?)... Get your hot pokers out and start punching holes in this....

My recent posts are concerning problems with an over firing VC Encore 2550 CAT . I have read what everyone has written and have checked everything to check. I have one last gasket to replace (Swestall's recommended damper door on the upper fireback which is a bit of a pain) and replaced my secondary air probe assembly (which after pulling out the old one, it wasn't as bad as I thought... Was actually in very good shape).

So, after reading some recent "My CAT doesn't seem to be working right..." threads, I decided to go out and look at my "smoke." What I believe may also be occurring is that my CAT is done. Although physically in good shape, at year 7 of moderate burns, it is just about shot. More smoke than usual although not dark. Yes, some of the smoke may be leaking through my upper fireback if the gasket is not good (but my damper feels like it always felt...).

So, I have contacted my dealer for the umpteenth time to double check the following and actually was able to speak with someone at VC. Here is what VC told me... "It sounds like your CC is shot... Your stove may be over firing because the CAT is not lighting off... The gases that are not going up the flue are concentrating in the body of the stove and burning off inside the stove rather than in the refractory. The body of your stove is actually getting hotter because the wood is burning faster AND the gases are burning in it rather than at the CAT and in the refractory. The fact that since the CAT may not be working, you are getting a stronger draft which is probably drawing a bit more air than normal through your closed primary air (yes, you will always get some air coming in the primary even when fully closed) and also through the always slightly opened secondary air thus it is adding more air to the stove and the cycle continues until your fuel depletes and then the stove cools down rapidly because there is no longer a lower temp catalyst to keep it going... So, you get this hot fire in the box, then it gets hotter, then it gets cooler when there is not enough left to keep the cycle going longer.... You add more wood, it remains cool, then heats up too fast (because the gases finally reach ignition in the body) until there is nothing left and it cools again..."

OK, opinions???? I am waiting to hear back from my dealer who upon inspection, found nothing wrong with the stove and my gasketing work was sound.

AGE
 
Sounds like it's time for a new cat. I think more smoke, shorter burns, and no glowing from the cat is a sure tell sign of cat replacement.
 
Yeah, the shorter burns are not my concern at this point but the hotter than normal burns and seemingly over firing condition. Just got off the phone with Sud Chemie and their tech folks said that there may be greater draw if the CC is not lighting off yet it is in physically good shape and not clogged (and my CC is both in good physical shape and clear right now). So, yes, it's time for a new CC anyway.

Keep the fan mail coming folks....
AGE
 
Nice to see we have come back around to this.....
 
If your cat is 5 years or so old, then chances are that you need a new one. In many cases, the cats break physically before they break chemically (stop working), but yours can be an exception.

The cat glowing does not mean much, as it only does this at a very high temp and when lots of gases are present. One way to tell would be with a probe above or in the cat. If you are getting temps of 1000 plus at many times, chances are that the cat is working because it would rarely hit that temp if not.

I have a new podcast conversation with John Gulland that I will be putting up in the next day - interestingly enough, he talks for a short while about the Encore and why he does not like it......not that it does not work, but that he feels the use of the thermostatic controls "insulate" the user from the actual wood burning experience (trial and error) and that he has seen folks use Encores for years and not really know what is happening. I think that is somewhat true in this case - the lack of simplicity and direct cause-effect from the air control makes it harder to know what is happening. The other end of that, of course, is that when it works perfectly it is very user friendly.
 
Considering that the average life expectancy for a correctly used cat is 4-5 years of fairly constant use or around 12-13000 hrs, I'd say you've done good and regardless of whether this is the reason for any overfiring you are experiencing or not, it's just plain time for a new one. Seems to me the VC rep has an argument that is at least plausible.
 
I like plausible. Plausible is ok by me. My new CC-257 is on the way and I should have it by Wed or Thurs. I hope to that magically this puts my entire VC issue to rest and I chalk up another lesson learned and "whodathunk" moment. Thanks for your input.
AGE
 
Hey there! Not bored, just glad we got back to it....
 
And the verdict is in... new secondary air assembly and new CAT... And it's behaving like two days ago. No rumble, a bit more smoke than I expected, more flame than usual and moving more than usual - even with the primary completely closed, and a hotter than "normal" giddle temp pushing 700 with only two small splits. Sigh...

So, it is heading to the 30s this weekend and time to take down the stove pipe and peer down from above -- and while I am at it, replace the damper gasket. Then, it is back to square one. I am so sad...

AGE
 
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