Question: Would you have an idea of exactly how to measure by temperature. whether or not the catalytic combustor on a Vermont Casting Intrepid II is working well or not ? I can't see exactly where one would stick in one of those probe-type thermometers. Can some sort of surface thermometer do the job ? Any technical details you know of will help. Vermont Castings has been most unhelpful. They say, "just look for a lack of smoke". While this may work, the technician in me wants to measure it. Answer: I assume that you have removed it an inspected it visually. Also, use a can of air to blow the dust off of it. If it is less than 5 years old, and physically together, chances are that it is good. They tend to degrade physically before they degrade chemically. Actually, in theory, the catalyst never gets used up - but in reality the thin coating can peel, be coated with dust or the ceramic substrate can break down. Excess smoke or creosote in the chimney is one way to know. The other is less heat output on the same wood load - compared to what you were getting in the past. Depending on the age of the intrepid II, there may be a small chrome removable cover (about 1/2" in diameter) where a probe thermometer can be inserted...or an area for an electronic probe (thermocouple). If you go this route, look for temperatures exceed 1000 degrees on top of the catalyst. This would almost surely mean that the reaction is taking place. A healthy catalyst starts working at temperatures as low as 400-500 degrees, but will quickly heat up as more fuel (smoke) is fed into it.