Loco is returned to service.
The loco was built at Boston Lodge works in 1979 and last ran in 2012 on the special train that carried the London Olympics Torch.
Engineers have converted the loco to coal firing after having originally been constructed as an oil burner.
An FR spokesman said: "The loco was outshopped in works grey and is likely to remain in this livery until at least the autumn.
"David Lloyd George will be used for the heaviest trains, along with sister loco Earl of Merioneth, while Merddin Emrys - originally built at Boston Lodge in 1879 - undergoes overhaul having been in daily use throughout 2013."