It's not just BG "engineers" that are full of it, when the pump on my boiler went I got in a local plumber heating "engineer" to replace it. He was very full of it, telling me all sorts of things that were obvious rubbish and eventually told me (after I watching him cross-thread one bolt...) the hex bolts on the pump were a special size and his hex key set cost him £100 and couldn't be bought by the public. After he'd replaced it but yet to fit the cover back on, he disappeared for 10 mins to take a phone call. So, knowing he was a billy bullsh*tter I popped open my toolbox, took out my hex keys to see what odd size is unavailable to mere mortals. Eyeballing the bolt, I nailed it first time and found the 5mm key fitted. That was the first and last time I used his services.