Boiler installation/costs?

Boiler installation/costs?
I have a conventional Baxi boiler with a hot water tank that I am considering upgrading with a more efficient boiler. I live in a 4 bed house in sheffield, there is a power shower in one of the bathrooms but our hot water demands are not high. I get confused about the condensing boilers, I understand that they can come either in a conventional format i.e. as a separate boiler and hot water tank or as a combination boiler.
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boiler installation Maidenhead|boiler service Maidenhead

I'm a graduate in Electrical Engineering as my BS and now I have admitted in three different major as listed below. I'm not sure which one is better for my future job opportunities. Please help me if you have any idea.
Energy Engineering - University of Illinois
Engineering Management - New Jersey Institute of Technology
Quality System Engineering - Concordia (Canada)
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Energy conservation