Furnace shuts off a lot with a code of 3 indicating pressure switch... furnace is 6 months old. Could the pitch of exhaust be causing problem (i.e. 1/4 " per 12") orthe three 90 degree elbows in the line? Furnace id 7 feet from outside wall for exhausting...

Hi Wallykap

Reasonable questions, for sure! Without knowing the furnace model and the fresh air and exhaust pipe type and sizes I can't answer in any way for certain, but if the furnace is 7 feet from the wall (i.e., probably 10 liner feet if include the vertical piping) and was professionally installed you are probably OK with elbows and distance...I hope.

With that being said, troubleshooting furnaces is a very difficult thing to do online via text messaging back and forth like this. I'll save you some real time and hassle here and just tell you to contact the manufacturer of the forced air furnace...talk to the technical services department. Here, have the model number and the serial number of the furnace handy and have a basic electrical tester handy (or even better, a GOOD quality one). These tech. departments are very efficient at walking you step by step through problems like this...;) They'll focus you in on the problem part/issue 5 minutes or so...I promise!

Good luck!

Mark