Gasafe guy I work with had a claim on him last year, alleged leaking joint thro' floor needing a brand new fitted cupboard downstairs, carpet etc etc. Never got to see it himself, insurance paid out and put his premium up a thousand a year afterwards.
Air lock after draining a rad is a probability, pressurise the system yourself afterwards and if anything pops off or leaks, even if knackered and old, anywhere else in the house, you will be held liable.
I'm very capable of doing the job, I'm even good at bending piope and solderering, but when decorating my own housing association home - called in a friendly plumber & paid him.