I would suggest not using condensing boilers . That is just my opinion though .
Great advice. All new boilers fitted from 1st April 2005 have to be condensing boilers where it is possible to fit one. It's the law, not a choice. I've never yet found a house where one can't be fitted one way or another.
The guy you used must have been a donkey to agree to sign off a boiler he didn't fit. Tell me, have you recieved a building control compliance certificate from Gas Safe ?