Train doors at the Front DT car was doorwere not proven closed. TC recycled train doors a few times but to no avail. Staff (DBG) assisted to isolate Front DT c ar A3 door for train to depart. ~~~~~ Train doors at the Front DT car was door     FC-059 A3 door encoder fault.No FOD found. DCP swap to B3 door.Function test ok.Door operator replace and function test ok.Push pull ok,Mating strip ok within criteria.DLS red line visible,Door cycle and static test ok. #3640-door operator:- Old s/n: 1506W0300115010 New s/n: D18YF0085001 Not: 2442034 raise. Done by Koh/Sateesh. 05/12/22