More tips for the WP24 and WP18 Door lifts straight up off the hinges to remove it. Don't unbolt the hinges. The four bolts on the drop chute cover allows the hopper to slide out the rear. Get those electrician's wire marker stickers before unpluging a bunch of stuff. Grind one link out of the auger drive chain if the chain adjustment is maxed out. The insulated firewall/bulkhead thing is held in by two bolts from inside the burn chamber. When re-assembling the heat exchanger with the metal hoses use drier vent hose clamps and tighten the heck out of them. I recommend re-tapping the 1/4"-20 threaded holes and wire wheeling all of the bolts. A complete, thorough cleaning means a disassembling of the combustion fan assembly, room fan assembly and the draft conrol butterfly valve. All of this gets hand scrubbed in the sink until it looks like new. The heat exchanger would also be completely removed and blown out with compressed air and shot inside and out with a hose or pressure washer. Brace yourself for some real time consuming work. This is easily a 12 hour job, certainly no less, probably way more.