De Dietrich DTG 1300 Eco.NOxPlus Serie Mode D'emploi page 17

1.2 Reversal valve motor - Type B
the black wire on the reversal valve motor is connected to the
live terminal on the transformer.
2
DTG 1300-.. Eco.NOxPlus, GVR 140-.. Condens 12/07/07 - 300002763-001-C