Ah well, you KNOW, beyond the SLIGHTEST doubt when your BG man says
"You need a powerflush or I won't mend your boiler. £650 please"
I know you are pretty good Chris. You must be as I have no idea how to put “KNOW beyond the SLIGHTEST doubt” and “because a bg man says” in one sentence.
My record still stands at finding the problem in under 10 minutes where 13 of bg’s finest had not managed. Granted, it was a very difficult fault as you had to look UNDER the boiler to see the residue leading to the faulty washer.