In parallel, four Stuttgart trains of the seventh series were relocated to Frankfurt in July 2009. After the main inspection, three of them were initially deployed from mid-June, primarily on the S7 and the airport short-commuter (S8 / S9), later normal in mixed operation with older units on all ET 420 rides. In the spring of 2014, another train of the seventh series and four trains of the eighth series were relocated from Stuttgart to Frankfurt in order to absorb a shortage of vehicles resulting from deadlines in older 420s. This was also the only period in which the eighth series in Frankfurt was in use.