it usually is boiler off the wall, some can be removed without lifting off but the other option is, is there a return heating pipe somewhere where a remote vessel could be fitted instead baring in mind its about the size of a football maybe bit bigger but can be located out the way with a bit pipe visible going to it.
The above is a much cheaper option providing vessel leaking means its knackered and keeps emptying outside rather than faulted and leaking internally from actual vessel itself.
ste
December 2009