The Mrs. was getting ready for her 3rd shift job last night and mentioned she smelled smoke...I thought maybe she had just blew out a candle but she said no. I went down to the basement and right away I smelled smoke and an odd odor. Turned lights on and could see smoke in the air near the boiler and mainly around the 8' insulated horizontal run of pipe to the chimney. I noticed my stack thermometer was pegged too(only goes to 500). Looking closer I could see the high temp insulation was smoldering and the pipes were cherry red! The high temp silicone sealing the pipes had disintigrated in several spots and one area actually had flame. Panic set in, quickly removed the insulation and smothered any flame. Ran outside to check the chimney...could not see anything and the chimney was cool to the touch....whew! I took the time to clean the pipe run into the chimney thinking maybe the 90 degree elbow at the bottom of the chimney was plugged with ash but I didn't get much out of it. Went and cleaned the boiler and since everything had cooled down I loaded up some wood and she ran fine all night. It took awhile for my nerves and the dogs to calm down though. A week or so ago I purposely let the firebox burn the coals way down and it seemed it was getting a bit too thick with them and I noticed that the stack temp had hit 500 while doing this. I knew last night that the box was needing wood soon but was stretching the reload until bedtime. What is causing such high stack temps when I'm down to coals and the unit is running? Normally it runs no higher than 425 but more like 375-400. I hesitate to put the insulation back on the pipes now...had originally done this to prevent an accidental burn and to keep the chimney hotter to lessen any condensation.