Brother HL-3450CN - Manual (Page 142)

CHAPTER 5 MAINTENANCE
5-26
16. Press Set, and then press Go. The printer is now in the READY state.
! Caution
Please be careful when replacing the Fusing Unit. Do not place pressure on
the Fusing Unit; it should fit in easily. If it does not, make sure the Fusing Unit
connector is free to move.
Do not apply force! It could damage both the Fusing Unit and the printer.