Chuck, you can still use the Aqua Hot for heat. The boiler is still full of fluid, and the fact that the domestic water coil is empty (or partialy empty) will not hurt it. It would actually be better for you to keep it turned on, since opening the low point drains doesn't really get all the water out of the coils. I never winterize my coach because I live in Florida, but when it even thinks about freezing, I keep mine turned on electric to make sure it doesn't freeze. If it does, it's a replace, not repair situtation.