how can I fix / replace?

I have a cosalt static caravan that over the winter period has had the water turned on by some misfit after the usual drain down I perform every year. The result is the heater pipe(s) have split water everywhere, the heater is a Paloma ph-5-3f mk5 can the pipes be resoldered as a permanent repair or alternatively I've been offered a ph-5-2f in pristine condition does anyone know whether this can be used as a direct replacement for the 3f thanks for any help Terry