1 ) WHICH COMBI BOILER? [NB this list is highly contentious and changes rapidly as new models show their colours] ***Since this was written, opinons whave swayed around, so the list has been removed.*** To get the correct size boiler use the Boiler Sizing Wizard OR Boiler Size Calculator When replacing a boiler, the quality of the installer AND the quality of the installation always determines how reliable the boiler will be. Also, it is imperative that the system is properly flushed out and installed by a Gas Safe fitter. Equally important is to protect the system with a good quality inhibitor such as Sentinel or Fernox. Inhibitor strength should be checked annually, and redosed every 3-4 years. Good practice to have your boiler serviced annually too.