Commuters faced morning rush hour misery after five lines were either suspended or hampered by delays.
London Overground commuters were particularly affected, with three of its routes hit by massive disruption due to faulty tracks.
There were severe delays on the Stratford to Richmond/Clapham Junction line, as well as between Watford Junction and Euston.
Earlier, faulty tracks had also caused the Gospel Oak to Barking line to close.
Meanwhile, a signal fault in Aldgate caused severe delays on the Metropolitan, Circle and Hammersmith and City lines.
The Bakerloo line was also impacted by minor delays due to a track fault.
