Yellow Flame - Gas Appliances

A yellow flame on a gas hob burner is caused by incomplete combustion due to a lack of sufficient air, often from clogged burner ports or an incorrect air-to-gas ratio. This can also be caused by dirty burners, blockages from spills or debris, or issues with the air shutter or gas pressure. A yellow flame is less efficient and can produce dangerous carbon monoxide. 

Dirty or clogged burners: Food debris, grease, or soot can block the small ports where the gas exits, restricting airflow and causing incomplete combustion.

Blocked burner vent: Residue or rust can accumulate in the vents or burner assembly, blocking air intake and leading to a yellow flame.

Gas Pressure: Incorrect gas pressure, often due to a faulty regulator, can disrupt the proper air-to-gas mixture.

Gas burner placement or damage: If burner caps or heads are not seated correctly after cleaning, it can affect airflow and cause a yellow flame. If the burner parts are warped or deformed the same thing can occur.

Stove Gas type: If a stove meant for natural gas is used with an LPG supply, it will produce a yellow flame because the fuel mixture is different. 

Here are few things you can try:

Clean the jets and burner parts.
Remove and refit it.
if on LPG, change the bottle.