Not familiar with this design, my ash pit doors are all simple hinges. I am going to take a wild guess that the weight used to pull the door shut is hung up some how. The wild guess is this is a system designed to let you know the ash pit is full, that is the weight is resting on the ash in the ash pit and cannot pull the door shut. Of course I could be very wrong in which case I have no idea whatsoever. My clean out is located behind my water heater and its a pain. I just wear old clothes, a dust mask, open the door and cleanup the flowing mess of ash. Good thing I only need to do every 5 years or so.

Are you talking about the fireplace DAMPER at the top of the firebox? You may have had some debris from above fall and block the damper plate operation. If this is what you are talking about you may want to have the fireplace inspected. Old chimneys can deteriorate over time and are frequently overlooked. Get a Certified Chimney sweep in to look it over

have you ever had a professional chimney expert not only clean it.. but also bring it up to specks???

if not.. it might be one of the best investments you can make.. to insure you do not burn down your beloved house ...

both times i bought houses with fireplaces ... it was the first thing i did.. come burning season ..

see link for an example of said service ... though i presume you arent in MI/OH ...

ken

Here is a link that might be useful: link