hi, I,ve just received one of the last 383L+ OSC, One of the problems i'm having with it is frosting. After taking advice I removed the plug and put it in the boiler room for 48hrs, then I replaced the tablets with new ones. When I tested it again, @-20, the frosting was still there but it gradually disappeared over a period of 15mins, is this normal or is 48hrs in a boiler room not long enough?