I have got to say what stem has written is just rubbish
Are you a politician?
By the very fact that combination boilers are sealed they are 20% more efficient than a conventional system.
I could if I had the time pull apart all your points, Where did you get your information from?
Both...
If the system is really that old it sounds like it may need a powerflush, I would recommend this anyway from the sounds of it and them perhaps change the pump.
If you can stop the center impeller on the pump, by taking out the center screw and placing a screwdriver on the nut, then change...