Well, I've had over 30 years experience with the various products, been on all the health and safety/gas safety courses etc, plus full disclosure CRB cert required. I don't think any particular PAPER qualifications would be required these days though. You'd need to be a good all-rounder who understands how buldings are put together, plus a knowledge of building regs. Good communicator, able and willing to work in all weathers, odd hours, weekends too....supply all your own equipment (like a Borescope, ladders, drills, etc, own transport and associated costs), commission only... usually.