A train has run over an obstruction on the line near Harpenden, which disrupted Thameslink trains between Luton and London St Pancras.
The Thameslink train hit a branch at around 10.40am today (Sunday, May 22), which was stuck in the air conditioning system.
A spokesperson for the train firm said there were 15-minute delays on the line and cancellations, but the line has since reopened.
The Thameslink spokesperson said at the time: "A train has hit an obstruction on the line between Luton and St Albans.
"The affected train has hit a branch and this is now caught in its air conditioning unit.
"It is not safe for the train to keep moving forward, meaning that one of the lines towards Luton is currently blocked.
"The train will stay in platform two at Harpenden whilst it awaits response teams to remove the branch.
"Other services will be able to go around this, however will pick up delays due to crossing over lines.
"Services that usually run between Sutton and Luton will now start and finish at St Albans.
"You will be able to change at St Albans for a services further north."
The issue was resolved at around 12.30pm.
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