This furnace was installed in 1990 or 1991.

I'm having a problem where the furnace is not firing. The inducer motor runs for about 20-25 seconds then shuts off.

I'm troubleshooting all the safety items to see if something there is causing the failure to fire.

The pressure switch has two vacuum hoses going to it. One goes to the condensate box and the other to the burner enclosure. Should the pressure switch hold a vacuum/pressure from both connectors? I can suck/blow into the hose going into the condensate side of the switch and it holds vacuum/pressure. When I do the same on the burner enclosure side of the switch I can hear an air leak in the switch and it does not hold vacuum/pressure. Is this normal operation or is the diaphram shot in the switch on the burner side?

Thank you.

Scott