IGNORE C/H OUTPUT?????? are you out of your mind???
If you do this you could end up with a lovely hot bath but not very hot radiators. The best thing you can do is get an expert i to quote what you need. If they are a reputable installer they will be more than happy for you to purchase the boiler as they wont have to put it through their books for a start. The only problem you might have is more and more companies wont sell to non gas safe registered people anymore.
boiler bill, January 2011