My central heating and air unit stopped putting out warm air last night. I woke up freezing. The blower will still run but no warm air will come out. What steps do I need to take before calling a repairman?

My central heating and air unit stopped putting out warm air last night. I woke up freezing. The blower will still run but no warm air will come out. What steps do I need to take before calling a repairman?
I had the same problem. The problem was the flame sensor. I have to clean it every year. Shut the furnace off at the switch on the furnace. Remove the flame sensor and clean it with an emery cloth. Re install it and turn the switch back on. Make sure all the covers that you remove are put back in place before you turn it back on.

My central heating and air unit stopped putting out warm air last night. I woke up freezing. The blower will still run but no warm air will come out. What steps do I need to take before calling a repairman?
Where might this flame sensor be found? I have a carrier unit.

It will look like the one below or similar and be located near
The burners tips...

http://www.mobilehomerepair.com/media/img/nordyne/632396.jpg

You may only be able to see the back half of it which is the part with the blade on it for the electrical connection. It'll be held in with a hex head (probably) screw.