Consolidated furnace about 9 years old. I was informed that my heater isn't working so when I looked at the codes on the furnace I saw the light blinking 4 times which meant air circ.problem so I unplugged the unit and plugged it back in and it fired up. I let the unit circulate about 4 times and then it didn't come back on so I checked it again and now it is showing a primaru limit circuit open alarm. I really don't have the money right now to pay for someone to come charge a lot of money so can someone please help me with this. My elderly mother is living there and it is suppose to get in the 20's tomorrow.Oh by the way would the filters on the furnace cause something like this?I don't know when they were cleaned.

Primary limit circuit faults are usually caused by overheating - usually caused by clogged air filter(s).