The drawback to a combi boiler is that they are generally alot larger that a standard one, so may not fit the space you have.
You must have had a terrible time with no hot water and heating for 8mths. Why have you waited so long to get it fixed? It would have driven me nuts!!
As the boiler is 15yrs old it may not be repairable, as the parts are possibly obsolete.
I'd agree with secretspirit...get a qualified engineer to have a look first, then decide on the options available.
good luck