My trusty Vermont Castings Vigilant 1977 has developed a problem (which isn't bad after 16 years of mostly trouble-free service). The damper will no longer stay in the closed position - when you turn the handle from horizontal to vertical to close the damper, it springs back to horizontal under the weight of the damper door itself. Whatever 'catch' there was before to keep the damper closed is no longer working. I've examined the thing as closely as I can, hoovered it all clean, checked for obstructions, but can't see what the problem is. At the moment the fault is erratic but it seems to be getting worse. I have improvised a stick to wedge the handle in the closed position as a temporary work-around, but would be interested if anyone can shed any light or offer suggestions.