To avoid frost damage when you leave your boat for the winter, you'll want to drain your pressurized water system. It only takes a short while to do, and may save you a lot of money.
The easiest way to winterize is to turn the pump off, open the taps, and let the water drain out, then open the drain valves to empty the rest of the water. If your system doesn't have drain valves, disconnect a pipe joint at the lowest point in the system, and let it drain. You may also need to drain the hot water storage tank and the pump supply tank separately. Before leaving, check to be sure you've drained as much water as possible.