I've had good service from OpenReach
Perhaps it's unusual but I had good service from OpenReach. I had an intermittent fault on my line which caused the ADSL carrier to drop and forced the modem to re-sync. I logged the fault with my ISP who did the line checks and said everything was fine. But they were happy to book an engineer if I was prepared to pay the cost if there was no fault.
I logged ping calls to my ISPs gateway using the BT test socket every 10 seconds for several hours to make sure I had the evidence and booked the engineer. The engineer duly arrived and put the diagnostic tool on the line which reported no fault. I showed him my log and he was happy to stay and watch it for a while based on the evidence I had collected. Sure enough the carrier dropped and re-sync'd but the diagnostic box didn't react at all. It kept reporting no fault but we'd both seen the carrier drop and re-sync.
He looked at me and said "I've never seen that before" and then spent the rest of the day tracking and replacing every joint in my copper cable back to the exchange. He then changed over the copper pair I was using on the main cables finding the best quality pair that wasn't in use. After many hours of work he discovered a bit of the exchange equipment had a fault and needed replacing which happened after 2 days and everything has been fine since.
When I was stood on the school playground picking up my daughter a few days later I was chatting to the parents who all said they'd noticed the broadband had stopped dropping out on them all the time. They hadn't called it in because they weren't confident that the fault wasn't their problem and the £180 charge for an engineer callout made them live with the unreliability.