The Blaenau branch is a 150 vice 197, too.Unit shortage. There looks to be 5 197s that have been stopped on Chester for at least 5 days, one of them since late September.
That's why the Bidston is a 150 today and the Crewe-Chester shuttle a very unusual these days pair of 153s, it was also a 158 the other day.
Once more units are introduced a small amount waiting repair shouldn't be as obvious as It currently is with a relatively small fleet.
The thing is, in TfW terms 197s aren’t a relatively small fleet - they’re the largest. And reliability is currently not good. Hard to see how increasing fleet size but maintaining them at the same, small depot will improve overall availability.