Problem solved! Spark arrestor screen at chimney top was gummed up. Cleaned and inspected down chimney. All is now well and fire is going great.
OK. I had that problem when we first put the stove in, using an old stovepipe system we inherited from a former owner.
My son-in-law's brother cleaned the chimney for us, and found that the spark arrester screen was clogged with soot. That's common because the metal is coldest up at the top. We simply cut out the screen, since the stove pipe is three stories up and there are no woods or dry brush anywhere near the house if a stray spark ever manages to get near the ground--which I have never seen happen. No problems with clogging at the top since then.
Whether or not you want to do that depends on your own choice and judgment. Is there anything nearby that might get set on fire if an unusually large spark got out?
congratulations..I still recommend a thermometer for the flue if its exposed and if not for the top of the fire box.
Mine screws into the flue just above the collar on the stove, a Vermont Castings Vigilant or put it on the fire box as they have a magnet in them.
I was amazed and it showed me I ran the thing too cool and created more problems because of it.
PS:I have a bat or 2 squeeze into my cap each summer and I have a screen up there.