Here's a really, really dumb question, but could soap (or other residue) be reacting with the hot FO and wax to produce foaming? I know, without a picture it's hard to diagnose, but I've often wondered if my candles would foam if I accidently left soap in them after cleaning. BTW -- never had a foaming problem when I was using C-3. Some bubbling once in awhile around the edges, but that's it. (even with Spiced Cranberry from NG)