Yes I could spend all night telling some of the tricks BG get up to, you get the odd good engineer but on the whole they couldn't care a tosh. They will keep taking you're annual fee year after year but when a repair is needed, new boiler is all their interested in, and dearer than anyone else on the planet.
A few years back when I was daft enough to have a contract they actually left the rear end of the bottom of the boiler hanging down. I could see the burners between the loose gasket and the casing, the only reason I found out just after he had gone was that the boiler seemed very noisy compared to normal, I knew he had been struggling, because you rarely have to take a hammer to repair a boiler. I used a mirror to look at the rear of the boiler as it was difficult to get at and see, there were 4 bolts that had not been put back. Hence the gap. I turned everything off, the two kids were in bed as it was about 7pm. It was the one and only time that I didn't care less whether this chap lost his job for neglect. I rang the emergency number and they were back before I'd put the phone down. The chap came back with others and admitted that he couldn't get the back bolts back in because the threads were shot. Then they put a notice on the boiler ( out of order do not use) I said are you having a laugh, I decided that 5 mins after you're clown left or my kids would have been dead, and me. They then said we will be back in the morning with a pack of new bolts. What a joke. NOT.
Previous to that, the 3 port valve was forever failing, heating/hot water. They came 3 times in 4 months, it wasn't until the 3rd visit I realized what they were doing. Each time they came with a 3 port diverter valve including the powerhead, they would just fit the power head onto a sized / hard to turn valve, in turn the power head would crack. I only found out on the third time because he forgot to take the new valve with him, so all along I still had the same valve, clogged up with muck and scale. Of course it takes seconds to replace the power head, but a little to much work to change the valve, THE REAL PROBLEM.