Baxi Bahama 100, strange problems?

We have a Bahama 100 running on LPG, it has been problematical, we weren't using hot water from the boiler (too long a story). Anyway, my better half wanted it connected, so I did, tap turned on, no water. Spoke to a friend of mine, who took a look, opened the valve to allow the hot water to flow, it did, at least for a while???? Then much to my dismay half of the radiators in the system stopped working. When I tell you we live in two static caravans (self builder) and we have been down to -12 overnight. HELP!!!!!!!!!