If the man was private deal or dealer then get back to him tell him telling him nothing b....y works.
Pumps do stick through lack of use so if your's is a drop in the barrel one outside the look at base of pump to see if you can access the impeller disc which sucks the water up into the system. See if you can turn it with small screw driver then turn it about 4 times then replace in quater filled or full water barrel try taps again, if flows you're away.
Once pump operational.
The boiler won't be 12volt heating. Ony uses 12volt ignition on gas.
I don't know of primus but I would assume it has built in mains 230/40volt immersion element[It works on electric he said] like the truma in my Lunar and Ralley, now before turning on the mains heating immersion the water in the hot tap from intial cold start must flow free to ensure the boiler is full, switching on before the boiler is full can damage boiter element unless it has an 'overheat button'
It would also pay to get a registered gas fitter to check the safe workings of oven, hob and caravan heater checked also electrics. Most dealerships with workshop have trained staff. Search yellow pages.type in caravan sales/repairs for your area.
Bob
April 2009