Earlier this year I found that the ring on the latch for my glass doors was frozen. The ashpan uses the same style latch so you might check and see if that ring is rotating. I freed it up with a pair of pliers and then disassembled it and polished the shaft OD and the ring ID.
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I would describe mine as typically "hard to latch" but that's pretty subjective, I have to work at it to get it to close, but it always does and has not broken yet in 10+ years..... You can adjust the clamping force by loosening the set screw and then backing off the nut a bit, try it out and then retighten the set screw. You want the ashpan to be tight, leaking air in there will certainly give you a raging primary burn.
FYI... I have the same stove as you, model 1975, but not the CAT-C version. Not sure what the difference is.....
- I bought mine new in 2012 and burn 4+ cord a year, 24/7.
- 8-10 hour burns are typical, 14+ hours is possible with air closed way down, but I rarely run that way.
- If you look in the 2022/23 VC owners thread you sill find lots of temp plots I posted for my burns. They may be of help to you in diagnosing the problem. Good burn
- Short burn times with a full load has to be either excess primary air (excessive draft or leaks) or you have low BTU wood (light, punky stuff)
- What are typical temps? Stove top, flue, cat? and how/where are you measuring them. Pictures are good....
- My chronic problem has been excessive cat temps, I routinely hit 1600+ cat temps in 80 - 90% of my burns. Still searching for a way to stop it.... I have rebuilt my stove twice with all new refractory and all new gasketing. Problem always remains the same.