The Stamford Marriott page on M.com notes that the pool is to be closed from 22nd - 28th October.

This was certainly up there a couple of weeks ago when I checked as I potentially had a meeting in the area to attend.

That announcement is publicity enough for me. I always double check hotels I'm staying at nearer the time if I book well in advance. It's inconvenient, but at least they have made alternative arrangements. Most hotels probably wouldn't have gone that far for a 1 week maintenence period.