Bloo
~ I learn something new ~ ~~~~ every day ~~~~

I've always used hot water from my combi boiler (well, not the thing in the loft anyway) - seemingly with no ill effects ?
not if you have several many gallons to do - it's not practical to stand and boil water (and add limescaleMaybe i'm being just stupid but can't you just boil up some coldwater and add that to you bucket of cold water to raise the temp.