Had my heating upgraded last month and spoke to three different installers-2 of them on Bord Gais approved list.I also wanted a condenser boiler but was talked out of it (baffled with techie speak) by these guys.One said he would not intall a condenser boiler into an existing system.He said u build the system around these boilers.They seem to be aware of problems with these things when put into older systems and convinced me it was a bad idea.
Finally went for a Gloworm Micron which is I am told is 75-80% efficient.
Its is a big improvement on what we had-can get decent heat in rads in around 20 mins.The old boiler seemed to struggle for an hour or more to do this.
BTW when I asked Bord Gais about probelms with condensers-I was told-"we are not aware of any issues with these"