I had not used my furnace over the summer. Before turning on the thermostat, I replaced the filter and checked to make sure red light was on solid. Turned on thermostat and furnace light started blinking error code 23, which according to list on furnace means pressure switch obstructed or off. I have not turned anything on or off on the furnace itself, and the pressure switch has the furnace cover protecting it. How do I fix this error, or do I need to have a professional come in?

Look around a little first,, more info would help,may I guess,is it a 90+ hi effecancy furnace? Fist thing I`d recommend is to check out your vent pipe completely,make sure nothing like a birds nest has it stopped up,I have on 2 different occasions found a blackbird had made its way all the way into the induction motor housing and that was where he spent his last few hours. Was a surprise to find it,, and furnace works fine.If you are cerain vent is clear,, then maybe call a professional, even though a little expensive is still cheaper than replacing parts yourself and still ending up calling someone

The pressure switch verifies that the inducer blower is running. Go to the sticky at the top of the forum, and read through the sequence of operations of a gas furnace. If something is wrong with the inducer fan or the pressure switch, it may be a simple parts replacement you can do.

If you do not hear the inducer motor running when you turn your heat on, you need to check the inducer motor. If the motor is running you have a restriction, It may be in the vent pipe, collector box or just a pressure switch sticking.(turn power off first) You can blow and suck on the small rubber line going to the pressure switch(Softly) you should hear it click. Turn the power back on and see if it will run.