I've used Jane Graham back in June when I was having problems with the boiler. She came promptly and fixed the issue and gave advice plus a permanent fix to prevent the same issue repeating next year. She's based just of Wandsworth Common.
Number is 07908 959937.
I used Steve at aquaheat as a result of this rec, but was a bit disappointed. I found him quite unfriendly and only really up for providing a general service, not resolving the specific problems that I was facing.