Mike
I've got an E1450, so it's not identical, but. Last year i started to see this (charcoal, creosote in electrical box) and thought nothing of it. Later, I had a boil-over. Turns out, the creosote was causing my upper solenoid to hang up, providing air for combustion even when there was no demand. At first, I suspect, it was just an accumulation where the solenoid flap rests on the pipe, giving just a little leakage, but eventually the flap didn't drop at all.
If this is what's getting you, it's easy to fix.
A couple of squirts of WD40 to the inside of the solenoid body, work it up and down a few dozen times, hit it with the WD again, work it again, until you can't get it to hang up at all.
I still get the occasional new appearance of creosote and coals, up to about 3/8" in size, in the electrical box; a couple of times I've heard a 'woof' when the furnace does a pulse, in between demands. I suspect what's happening is an accumulation of combustible gas in the firebox is suddenly mixed with a load of fresh air, and the available wood coals suddenly ignites the mix, resulting in a minor blast in the furnace which pushes 'stuff' back to the electrical box.
Blair