First Capital Connect says three out of four lines on the Thameslink route are now open, following overhead wire damage in the Radlett area on Wednesday.
This morning (Friday) a spokesman said: “Our services are starting to return to normal, however there will be residual delays and alterations.
“Please continue to check our website for further information and allow yourself extra travelling time.
“We will continue to work together with Network Rail to restore our service to normal. “Please accept our sincere apologies for the disruption over the past three days.”
A full East Midlands Trains timetable is now running.