Molten/fused ash shouldn't hold that 500* temp very long. And once the fan starts it will surely go cold.
Breaking it up was the best thing you could of done to the molten ash, as it will cool quickly that way.
On the other hand...very likely the you will have an out-fire too, as the fresh coal may not ignite if no hot coals are present and livened up by the fan.
Not sure why it happened though.