First experience, no problems, easier than expected.
My first interaction with a gas boiler service, having recently bought a property and receiving a letter in the post from 1st call to remind me that the next service was due (the service log did confirm it had been installed and subsequently annually serviced late Feb each year by this same company). I phoned up, and was able to schedule an appointment in the next week with great flexibility to meet my work schedule. I did later need to rearrange that and it was no problem (there was a slight mistake with the scheduling on their part, but it was quickly resolved). The engineer arrived on time, fully stripped and cleaned the boiler and performed some additional checks (the roof from outdoors and via the attic) and also answered a few questions that I had. Only, minor, complaint was that the engineer emptied something cleaned out of the boiler into the bathroom sink (black dust and dead wasps). They forgot to wash it down the sink, so I had to do that myself after they'd left.