We have a Tempstar furnace. The indicator is reading that the pressure switch is stuck open when it should be closed. The fan still kicks on but it won't light..

The reason the fan comes on is it is on a timer which turns the fan on "X" seconds after the thermostat calls for heat. I doesn't know or care if the flame lit or not.

There should be a small hose going from the exhaust blower to the pressure switch. Take it off the blower & suck very gently. If you hear the switch click, the problem is not with the switch. If the switch clicks, use a paper clip to clean out the nipple to which the hose connected at the blower & try the furnace again.