This seems to be the best thread to post this, as it could be entitled 'IEP can't come soon enough', but also affects the resulting cascade, possibly.
We travelled on GWR Mark 3 stock yesterday (HST Bath to Didcot and return) and were disappointed that on both occasions, our initial choice of std class coach was very stuffy on a hot day. This was due to the fact that some of the sliding doors were kaput (thus permanently open) and of course, as pax always leave the vestibule exit door windows open (to reach the door handle), the a/c cannot function. It was of course also very noisy in those coaches.
We solved this by moving to a coach where the sliding doors were functioning and there, it was pleasantly cool and also quiet. Of course in winter, the reverse would be the case, freezing. I did wonder whether GWR OB Staff are instructed to keep closing vestibule door windows and whether that would lead to a/c working. In other words whether the vestibule is part of the a/c area, I would assume not from the above related experience.
I doubt that they are so instructed, as we didn't see any ticket check staff either on the way or the way back.
I do wonder, even at this late stage, whether the repainting of stock in 'GWR' green is wrongly prioritised over repairing sliding doors on this stock.