Posted originally in Plumbing Section - Probably a better chance of getting response here
Similar posts always seem to focus on the issue of DIY gas work, whereas I have no intention of doing any. I believe there is still plenty of stuff a competent DIY'er could do without compromising safety.
Please advise if adopting the following approach would achieve compliance with current legislation whilst maximising the DIY content. Only steps 3, 10, 12 and maybe 11 done by professionals – I fitted the original vented system along these lines.
1. Size select and purchase combi boiler after research
2. Isolate boiler and drain system.
3. Engage Gas Safe Reg to disconnect gas and cap off away from work area
4. Remove old boiler, tanks and hot water cylinder along with interconnecting pipework (weigh-in at scrap metal dealer)
5. Replace all valves in central heating and hot water feed lines with valves more suitable for mains pressure – existing valves could be up to 30 years old
6. Replace any original radiators and suspect radiator valves - most have already been renewed over the last few years.
7. Mount new combi boiler on wall
8. Prepare flue route and fit loosely
9. Connect new flow & return, hot water supply pipework and cold feed to boiler via isolate valves
10. Power flush – don’t know how/who does this yet, so help appreciated.
11. Connect programmer etc and elec supply – yes I know I should use an electrician but I did rewire the house 15 years ago
12. Call in Gas Safe Reg to fix and seal flue, connect gas and commission boiler and system, and sign off work if satisfied.