A video I just watched had the guy using 12 wraps, probably will depend on how loose the fit is. I don't tend to run my CH much over 1bar as I have no idea what the joints are like under the floors so don't fancy popping them.
I don't see how it could be on the hot water circuit?
I was recently told that you need to be wrapping 20 turns for rad valves.
I thought towel rails are heated from the hot water circuit?