If the scuttle water is too hot, the lather will dry up too fast. Filling the bowl and chamber with hot tap water, letting the scuttle warm up, and then draining and refilling only the water chamber works for me. In the United States, hot water from a tap must be not less than 110°F (43° C) and not exceed 130°F (54° C).
You will have to rehydrate and remix your warm lather from time to time and find your best compromise between increasing lather warmness and the consequential increased frequency of necessary rehydration/remixing. Really hot water temperatures kill lather in the scuttle's bowl fast. I recommend watching the Chimensch 30th anniversary video where he demonstrates scuttle warming, mixing lather, and rehydrating thickening lather using his Schwatzweisskermaic scuttle. http://straightrazorpalace.com/shavi...ing-video.html
I believe that large scuttle mass and a large water chamber are really important for a leisurely SR shave with warm lather as small scuttles cool off too fast, unless one shaves fast. The scuttle will also work well to make room temperature lather in hot summer weather, just do not fill the water chamber. Large scuttles work best when left on the counter top in use, they are too heavy to hand hold. If you want to make room temperature lather, a bowl is smaller, lighter, and less expensive, and many can be hand held while mixing lather. I also use a nice decorative bowl from the local pottery shop for making lather at room temperature.
HTH