Irish Rail was bombarded with complaints from passengers after one of their intercity services ended up taking more than seven hours with most passengers not arriving at their destination until 2.30am.
In emails to the rail operators, members of the public wrote of being left standing in the pouring rain on a platform as they waited for another train.
The delay happened in February when a service between Dublin and Cork was hit by a “fatal failure” of a water pump, according to an internal investigation report from Irish Rail.
It said delays for passengers on board, and several other services also hit, were “very significant” and that lessons needed to be learned from what had happened.
The report also said that the line was likely to get even busier over the next few years so that standby locomotives and drivers might need to be in place at key locations to avoid similar incidents.
In a barrage of complaints and requests for compensation from passengers, one wrote of the “dreadful experience and conditions” they had endured on their journey.