How much you spend to buy a new boiler will greatly depend on who is installing the boiler. Many people believe that as long as the gas plumber/heating engineer is corgi registered (now changed to gas safe) then it is going to be OK but this isn't always the case. There's many cowboy plumbers and gas fitters out there that are going to miss bits off the quote just to get the job.
Clients believe that when they need a new boiler it is only a circumstance of the simple boiler swap. To the new regulations there is not any such thing as a straightforward boiler swap any more. All new boiler installations should be installed to the new power efficiency rules which means boilers finally have to be A-rated. A-rated boilers are more generally known as condensing boilers.
Cleansing away the old system is critical with modern boilers as the heat exchangers have a tendency to be so much smaller and may block up quickly. Power flushing the central heating is the best means and I would also guide in fitting a Magnaclean filter.
Many of the brand new boilers will need an updated gas supply pipe (something the cowboys ordinarily miss).
When installing a new boiler (the plumber occasionally wires this them self to conserve on costs not allowed a qualified electricians ought to be used).
Your installation could also need updating to a fully pumped system. If you have had your new boiler fitted you need to obtain a building regulations conformity certification. (you will want this to sell your house) So taking all this into account you ought to be aiming at paying no less then around GBP2000 for the work to be done (in case that it is less than this ask your self why).