Radiator on the roof?

So, the painting in the kitchen is finished. The plasterer is booked for Monday morning and I need to remove 2 radiators from the hallway and strip all the old wallpaper. 1 radiator off and time for a tea break. Whilst making a brew, I looked up and saw the walls were wet? Double take? Yes, the walls were wet. I ran upstairs and got out of the small bedroom window and checked the roof. I fear that it maybe u/s. What can I use too make a repair? Hence use of radiator and flashband. Roofers are booked for Aug 28th. With our weather, the kitchen could be an indoor pool! ffs