My furnace burner does not stay long. I had my pilot light goes out. I lit the pilot light and it works. And as soon as I put the wall thermostat on ON position for heat, I can see the burner starts with the normal flame. But after 30 seconds burner flame goes off as well the pilot light goes out too.
Somebody told me to change the thermocouple. I did not. Isn't the thermocouple for the pilot light if the pilot light does not remains lit?
Please help
Thanks

The thermocouple is a bi-metal appliance that when heated creates a small amount of electricity. This power then holds open a electro-magnet valve that keeps the pilot burning and allows the main burner to open, when called for, as long as the thermocouple is hot. These deteriorate from all the heat and need to be replaces at times.
This may not be your problem but it is a good place to start.

Bad flame sensor.sometimes you can clean it with a file.do not use sandpaper. Residue from the sandpaper will leave a film on the sensor.

I`ve never known anyone to use a file on flame sensor,, I use steel wool,, most older furnaces that have pilot lights ,that I`ve worked on don`t have flame sensors