miller furnace blower does not shut off

If the blower is running but the burner does not come on, it could be either a fault in the control board (blown fuse, no low voltage coming coming to power the controller or other electronics fault) or an open high limit switch. The switch is a round metallic part near the gas valve and manifold. See if you can open the control panel and check if there are any lights on it (and which are lit if there are any). As for the high limit switch - it may just need to be blown with some air to remove dust or its wires checked. Be sure to do all that with power turned off. Beyond that I would advise calling a pro technician.