You either burned out the new board, or the incline motor.
Test the board with a volt meter to see if its putting out any power when the incline is pressed.
If it is then replace the motor, if not replace the board.
If I disconnect the single INCLINE connection on the new board and switch on then the incline automatically rises to its maxim then will not lower. (Which is what inadvertently happened when I fitted the new board) When reconnecting the INCLINE and switching on the incline automatically lowers then will not move. Therefore I assume the incline motor is working. (The incline indicator on the control panel reads that the incline is moving up when selected when the treadmill is in this state.) The treadmill belt functions perfectly well and reacts positively to all the selections so I assume that the control board is ok apart from the connections..
Do you have it wired backwards?
Just because the speed works correctly has no reflection on whether or not the incline portion of the board is working.
try switching the wires and inclining it up