I have a high efficiency carrier furnace. When I came home yesterday I noticed that my house was a lot colder then it should be. The fan was blowing but no hot air. I checked the furnace and the LED red light was flashing - 3 quick then 1 long. On the back panel it said this indicated one of a few problems
1. Pressure draft safeguard
2. Auxilary-limit (when used)
3. or block vent shut off (when used)
4. switch did not close or reopen.

I checked outside to see if any leafs were blocking the intake and it seemed clear. Can anyone help with this as I would hate to pay for a service call when it could be something simple and easy enough that I fix.