DJH1971 said:
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It appears today's 07:38 MCV-LIV service consists of two 319s for some strange reason.
07:02 MCV-Liv cancelled due to unit fault, 07:38 took faulty train back to Liverpool so that an ECS movement was only needed from Lime Street to Allerton, opposed to from Victoria to Allerton.
The 0702 was apparently cancelled due to 'a problem with the on-board safety systems (M0)'. It seems the fault didn't disable the unit, but made it unsuitable for service. It seems to have been taken from Lime Street to Allerton at 0848, with the completely healthy 319 following as the 0848 Lime Street to Warrington Bank Quay (4L at 0852), the normal progression. There is a slight discrepancy in platform numbers, but I don't think there's any significance in that.
The unit which should have operated the 0816 Lime Street to Manchester Airport instead covered for the defective unit in operating 0820 Lime Street to Manchester Victoria, with the 0816 Airport and 0940 return being cancelled. It is usual (or, at least, commonplace) for the stopper to be given priority over the semi-fast in this way.
A unit seems to have been brought from Allerton at c.0920 (0940 into Lime Street), this then apparently operated the 1120 to Manchester Victoria, with the 1002 ex-Victoria doing the 1116 Airport. This is normal, the stopper and semi-fast are scheduled to swap duties at this point.
I'm inclined to suppose that the driver who should have operated the 0816 semi-fast was detailed to take the defective unit to Allerton, and bring a healthy one back. Shame there was (presumably) no-one available to fetch a unit from Allerton earlier.