Replacing gas boiler - BER C3 rating Just bought a house, built 2004, BER rating C3, 150 sqm detached. Ferroli Tempra 24 gas boiler, BER says it's 78% water and space heating efficiency. Two zones, i.e. two thermostats, upstairs and downstairs, no separate water zone. One of the four showers runs off hot water, i.e. it isn't an electric shower. Got an RGI to look at boiler, it hadn't been serviced, got it working, but the timer clock sparked. So now no timer. I would like to upgrade the boiler as I feel it's not the best. RGI recommended Viessmans, it seems he is a registered installer. He said something like the 5yr warranty is extended to 10yr if he installs it, and services it. He mentioned 2,500 for boiler. He mentioned adding third zone on water cylinder. This could all be a sales spiel, but they do seem like good gas boilers. My questions: (1) I read here that it's not much use replacing boiler unless house is well insulated. So am I wasting money on a new boiler with a C3 rating? (2) Should I try to improve C3 rating first? (3) Are Viessmanns a good boiler? (4) What model would I need for 14 rads, of various sizes. Vitodens 100-W or 200-W? What KW output? (5) I think I would qualify for the 750 boiler heating control grant? I really, really appreciate any advice.