Thameslink commuters have been hit by 30-minute delays due to problems at a depot between Dartford and London Bridge.
Fewer Thameslink trains can run between those stations and National Rail has told customers to allow extra journey time.
Disruption is expected until midday.
Earlier on Tuesday commuters travelling through north London were hit by rush-hour delays following a signalling failure.
National Rail warned a fault with the signalling system between Moorgate and Finsbury Park shut several lines, meaning Great Northern trains were cancelled or delayed by 15 minutes.
