Sounds as though Rollo has been down this road. Many of the newer coal furnaces utilized "rice" coal with automated feed augers and "shakers".

The theory is that fresh air passing through the grates from below keeps them cool enough that they won't warp. Quickest way to ruin the grates is to neglect cleaning out the ashes. An unfortunate occurance when the automated furnaces came on the scene; not having to "tend" the fire, it was too easy to forget to clean out the ash pit.

Jim

__________________
2005 C240 4matic wagon (daily driver)
87 190D - 225K (on loan)
85 190D - 312K (on loan)
2011 Subaru Legacy AWD (Wife's)