I need to replace a glow-worm Energysaver 60 boiler. Apparently the Heat Exchanger is leaking and I have been told the boiler is obsolete and the parts are unavailable. Would it make sense to replace it with a glow-worm 24hxi. I do not have a sealed system. I have the tank in the loft feeding a cistern. Would it be worth changing the plumbing and getting one of the glow-worm sxi range? or should I just leave the set-up the way it is and have a hxi fitted?