“Since entering passenger service, we’ve seen several technical issues associated with their long-term storage,” they added.
“Since the introduction of our May timetable, Class 175 issues have accounted for nearly 15% of delay minutes and around 14% of cancellations.”
Journey planners will be updated with the schedule changes in the coming days and customers with bookings on affected services will be contacted directly, GWR said.
Additional moves to help tackle the problem will include trains undergoing extra assurance checks before returning to service after repairs.
GWR said each train would be required to complete 1,000 fault-free miles in simulated passenger operation before re-entering service.
It said a dedicated technical investigation team would be used to identify the root causes of recurring faults and strengthen maintenance arrangements.
Last month, GWR managing director Mark Hopwood said customers were “right to be disappointed” but said “we’re absolutely determined to sort this out”.
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