Hi all, First time poster trying to figure out a backfire issue with my woodstove. I have searched the web, and found many scenarios, but mine seems to defy everything I've read. I have a hearthstone Mansfield that is 4 years old. I have about 6ft of single wall pipe exiting straight out the top of the stove connecting to 16ft of double wall stainless chimney pipe. Everything was installed by my local dealer while the house was under construction. I only burn seasoned wood, and every two years I get my chimney swept which only produces a very small amount of creosote crumbs. Every season I change the seals on the door and ash pan door.myproblem started right after I changed the seals this year. I noticed the fire was burning a little faster than normal so I decided I better change the seals before it got too cold. Ever since I changed the seals, I can't seem to control the fire. It seems to rage out of control if I load more than a few pieces of wood. Anything more than 25 percent capacity and the fire takes off uncontrollable and starts to backfire. Tonight I'm pretty sure I saw a flame come out of the joint in the flue. My throttle was half open when this happened, so I opened it all the way which is what everything I read says to do. This did not solve the problem, so I closed the air control all the way, the fire slowed down, and the backfiring stopped. I suspect I have an air leak at the ash pan door, but shouldn't the stove be over firing instead of backfiring? Everything im experiencing goes against everything ive read on this subject. I've changed the seals 3 times in the past month trying to correct this, and I'm starting to think I may have another problem all together. I had this thing dialed in for the past four years and now I'm afraid to use it. If anyone has any ideas, I'm all ears.