I have a static caravan that is fitted with gas central heating. For 6 weeks each year I am not permitted to use the caravan (Jan - Mar) and all services are disconnected (gas, water & electricity). How can I protect my gas boiler from frost damage other than to drain it down each year or, is this the only option? I did not drain it down this year but spent the entire 6 weeks worrying about the boiler - fortunately, everything was ok.