In all, the ferry's service has been disrupted nine times from June 6 to July 2, including a run of three consecutive days late last month.
The 50-year-old Woolwich Ferry normally operates a two boat service with a third boat held in reserve. But one of the vessels is currently in dry dock being refurbished - meaning there is no back up if there is a problem.
General manager of TfL’s London River Services Andy Thompson, , said: "The Woolwich Ferry provides a vital river crossing in east London and we apologise for the disruption to service our passengers have experienced recently.
"We are currently undertaking work to extend the life of the ferry terminals and the three boats to ensure a more reliable service can be maintained in the future.
"We are working hard to minimise any disruption caused by these works, however, the level of disruption in recent weeks has regrettably been higher than expected."