I have an older Wait Circulator using propane in the garage.
It's a model NW50 which I have properly maintained over the years.
Just recently I removed the burner to clean it because it was burning yellow.
A hacksaw blade fits just perfect in the slots to clean them and just bow it out.
Now I have a nice blue flame but after a minute there is blowback and the gas ignites below in the burner chamber.
What should I do?

Puzzled!
Stan

Sounds like the burners aren't properly installed allowing gas to bypass the burner. If it worked properly before cleaning something was not done right on the reinstall. Make sure the burner isn't cracked.