Propane and Butane flame colours

[Dustydog]

My man cave Calor gas fire starts off with a lovely blue flame which after 5 minutes goes yellow. Not good. However I have cleaned the burners, vacuum cleaner. No difference. Is this a dealer issue or have I missed something stopping the correct combustion?

 

[Damian]

Yellow flames indicate the wrong burner mixture or damage to the burner bar.
Rust will cause this yellowing of the flame and the production of CO.
It needs a new burner .

Whilst you may have removed external rust you cannot get to the internal parts that will also have rust on them.