By your post im guessing you have a 2 story house.
Have a look at the boiler,water pressure guage.Should be between 12 and 15 psi 140 to180.f when running.
If its above or close to 30 psi the relief valve will open to let off the pressure,we do not want this to happen normally.
If you have high water pressure at the boiler you will need to go to the highest radiator or any one on the second floor and open the bleeder.Looks like this
Carefully open it slow into a bucket,let air out until you get a steady stream of water.Do this to all of the radiators,idealy using a bleeder key or needle nose pliers.This may take some time.
Once we can assume all the air is out,check your water pressure again should be 15 to 20 psi.If you have no pressure then your auto fill valve is bad.If you have 15 to 20 then proceed.
Raise the temp of the t stat to start the boiler.6 degrees above whatever the room temp is.
If you still are having problems your t stat may be faulty.If your boiler is at 15 to 20 psi 140 to 180.f and it still shuts down after 3 min your return pump may be bad.
Hope this is helpfull