Gas and Oil Home Heating Furnaces - furnace intermittent problem

My Propane furnace has started having intermittent problems. It won't kick in sometimes and the temperature in the house will cool off about 3 degrees. Then it will start up and warm up the house. Turning off the furnace and back on will always get it to start. Sometimes it will shut off after 5 minutes. In this case the fan and burner don't appear to ever start.

You have to catch it in the act and observe the sequencing of the furnace to see at what point there is failure of the sequence before ignition or if the is ignition burner flame, but it goes out prematurely.

Otherwise one can only guess. But -

- You can perform free routine maintenance items like check the filter, clean the flame sensor, make sure the condensate lines are clear, that all connections are tight (you can remove the connectors and slip them back on and feel if they are all tight, and by doing this you will be scratching into them a better connection. If any are loose, take a pliers and squeeze the spade connector flatter some, before slipping it back on). Make sure condensate water has not been leaking out of the inducer fan gasket or at bad pvc pipe glue joints and dripping on components inside. Make sure small rubber vaccum lines are on the pressure switch and other connection points good. Make sure outside vents and intake (if applicable) are clear.
Sometimes it will shut off after 5 minutes. In this case the fan and burner don't appear to ever start.