I have a friend whose furnace shuts down occasionally and when she pulls the door off and pushes the safety switch in by hand, the furnace starts back up and when she puts door back on it will work fine for a few days until it stops working again. This happens several times a week. The switch is making contact with the door. Could the switch be going bad or would something else make this happen?

By the way, It is a high efficiency forced air gas furnace and trouble light does not blink

It is possible the switch is intermittent or the door is not on tight enough to keep the switch activated.

It is also possible there is another problem. When you remove the door and reactivate the switch you are actually reseting the furnace circuit which resets the circuit board so another problem is being covered up by doing that. Next time see if the circuit board indicator is flashing before removing the door. The blinking or flashing is a message and the information for this is located on the back side of the blower door.