When I first got my CFX I hadn't got the ELBs yet so I vaped just using the oven. The inside of the oven got black and scaled up. I tried iso, scrubbing pads (Mr Clean Eraser), Smoke Soap, whatever I could.
I can not be responsible for the following, cause I can't control how you do it.
Run the temp up to at least 400f. A qtip DAMP, I repeat DAMP with distilled water, and steam the scale off. Make sure you don't get water in the bottom. Use distilled water. It doesn't have chlorine or minerals to be left in the bowl. If you do this on it's side, the scale will fall off. Just be careful and only dampen the qtip. Doc
I repeat DAMP, and as the water drys out re-dampen and squeeze out the tip repeat.