I have to grin every time I read one of these. I was a total DIY as far as HVAC (and everything else I could possibly do) was concerned not all that long ago. Started school only 32 months ago. I remember: deciding that our tstat must be bad one time when our system failed and changing it to no avail; taking our blower motor out and trying to clean it to get it to work; putting in a new thermocouple...each time we had to call a tech.
Now my favorite call is "my Tstat is not working properly..."