In the last part of my working life, I had eleven waste heat boilers under my wing at various sites. The next due inspection rarely coincided with a planned downtime, which was three to four monthly, so it was almost routine for me to request a Reg 9 extension to the due date. so we didn't have to shut down early. Now I'm just involved with loco boilers, I still request them from time to time when it is convenient to do so but you really have to have a reason for doing it, though. Do other railways ever do this? If you want to get back in touch with such things now you're a gentleman of leisure like me, it can be arranged. You'll just need to spend more time in Yorkshire.