Heat is an indicator there is too much current being drawn by the device. Either there is problem with the fan, undersized wire to the fan or switch, poor wiring connection, or a defective switch.
Since you just installed a new switch I'm assuming the wiring connections at the switch are not the problem. Might want to check the connections at the fan. Beyond that, looks like it might be a problem with the fan or the switch is not rated for the current the fan draws.
Keep us posted.
Edited by: pulpwood007