A problem with the scheme’s IT system meant users were unable to access bikes between 05.30 and 16.15.
TfL says no users were charged late return fees as a consequence of the outage.
Earlier this month Mayor Boris Johnson announced a doubling of hire and membership fees in an effort to plug the loss-making scheme’s finances.
Nick Aldworth, Barclays Cycle Hire General Manager said: “casual users and auto-renew customers were temporarily unable to hire bikes yesterday due to a problem with Serco’s IT operating system.
“Serco worked to rectify the problem as quickly as possible to return the system to full use. Whilst the problem was addressed users who had bikes out on hire, had a valid access period or annual members could continue to hire as normal. We apologise to customers for the inconvenience the outage caused.”