I was quite surprised recently to be told that there were bits of the airframe that could not be treated with anything but hot water, the area around the cockpit being one of them. The problem was that blowing snow had settled and frozen in this area and the only treatment was hot water to melt it, I had suggested using a brush to try and remove it. My concern was that having washed and melted it it off how quickly would the now damp area cool and freeze. No holdover time exists just for hot water and a visual inspection had to suffice.