If I have a Raywall/TPI furnace that isn't working, is there anything I
can do and or check to get it working again other then call a tech?

The Thermostat seems to work ok. The furnace fan pushes air normally,
but the air ins't getting hot llike it used to. The air out of the vents
is kind of warm but wont get as hot or warm like is used to. It seems
that the furnace just runs and runs and wont shut off without getting
the house warm.

Please help