catmando if you google government boiler scrappage you will find out that its only for G rated boilers or worse so if you have correctly identified your boiler and thus your rating, you appear to be a long way off.
the Corgi trust in their recent report on CO deaths and comparisons over the last decade specificially state that in boiler related incedents, boilers over 16 years old or more have a 1.6 times the risk of being involved in a CO incedent compared to newer boilers.
now a cynical person might say that is scare mongering to create sales but they do have a point
i think that your unit at a design age of say 17-20 years can,t compare to todays B rated boilers and i would change it for a more efficient, cheaper to run boiler. i certainly would,nt spend money repairing it.
however i cannot fault you for trying to saving money,
you are not over 60 by any chance, if i may be so bold to ask? if you are google warmfront heating rebate