A healthy gas burner flame should be blue — steady, cone-shaped, and burning cleanly. If your flame has turned yellow or orange, it's a sign that the gas isn't burning completely, and in some cases it can be a serious safety concern. Here's what causes it, what you can safely check yourself, and when you need to pick up the phone.
What a Blue Flame vs. a Yellow Flame Means
Gas burners are designed to mix gas and air in precise proportions before ignition. When that mix is correct, combustion is complete and the flame burns blue. A yellow or orange flame means the burner is getting too little air (or too much gas), causing incomplete combustion. Incomplete combustion produces carbon monoxide (CO) — a colourless, odourless gas that is potentially fatal. This is why a persistent yellow flame should never be ignored.
A brief flicker of yellow at ignition or at the very tips of a blue flame is generally normal. It's a consistently yellow or orange flame across the burner that signals a problem.
Common Causes of a Yellow Gas Flame
- Blocked or dirty burner ports — Grease, food debris, and spills can clog the small holes around the burner head, restricting airflow. This is the most common cause on cooktop burners.
- Misaligned burner cap — On a cooktop, if the burner cap is sitting unevenly after cleaning, it can disrupt the air-to-gas mix.
- Incorrect air-shutter setting — Gas appliances have an air shutter (or air inlet) that controls how much air mixes with the gas. If this has been disturbed, the mixture goes out of balance.
- Wrong gas type or pressure — New Zealand homes use either natural gas (NG) or LPG. Appliances are set up for one or the other. Using an appliance on the wrong gas type, or if the regulator pressure is incorrect, will cause yellow flames.
- Partially blocked flue or ventilation — On heaters and ovens, a blocked flue restricts the oxygen available for combustion.
- Faulty or worn injectors — Over time, gas injectors can wear or become partially blocked, altering the gas flow rate.
What You Can Safely Check Yourself
There are a few basic checks a homeowner can do on a cooktop burner before calling a tradesperson:
- Turn off the burner and let it cool completely.
- Remove the burner cap and crown. Check for visible food debris or grease blocking the ports.
- Clean the burner ports gently with a soft brush, toothpick, or a pin — never a toothpick that can break off inside. Avoid enlarging the holes.
- Rinse and dry thoroughly before reassembling. Moisture in the ports can also cause yellow flames.
- Reseat the burner cap carefully, making sure it sits flat and level.
- Test the flame again once everything is dry and correctly reassembled.
If cleaning and reseating the burner cap doesn't fix the problem, stop there. Do not attempt to adjust gas pressure, air shutters, injectors, or any internal components yourself — this is restricted gasfitting work under New Zealand law.
Carbon Monoxide: The Hidden Danger
Incomplete combustion from a yellow flame produces carbon monoxide (CO). CO poisoning can cause headaches, dizziness, nausea, and — at high concentrations — death. If you notice a yellow flame alongside symptoms like headaches when using the appliance, or if you smell an unusual odour:
- Ventilate the area immediately — open windows and doors.
- Turn off the appliance at the isolation valve if it is safe to do so.
- Leave the building and call your gas supplier or a licensed gasfitter.
- Consider installing a CO alarm — Energywise recommends CO detectors in any home with gas appliances.
Safety note: Never use a gas appliance with a persistent yellow flame until the cause has been identified and fixed by a qualified professional.
What Is Restricted Gasfitting Work in NZ?
Under the Gas Act 1992 and its regulations, gasfitting work — including adjusting gas pressure, replacing injectors, modifying air shutters, connecting or disconnecting appliances, and working on gas pipework — must be carried out by a licensed gasfitter registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB). Unlicensed gasfitting work is illegal and can void your home insurance.
Homeowners are permitted to clean external burner components (as described above), but anything involving the gas supply, internal components, or appliance connections must be left to a professional.
When to Call a Professional
Call a licensed gasfitter if:
- Cleaning the burner ports doesn't restore a blue flame.
- Multiple burners on the appliance are affected.
- The yellow flame appears on a gas heater, oven, or hot water system — not just a cooktop.
- You suspect incorrect gas pressure or the wrong gas type.
- The appliance has recently been moved, reconnected, or serviced by someone other than a licensed gasfitter.
- You have any concerns about CO exposure or smell gas.
You can find qualified, licensed gasfitters in your area right here on tradedirectory.co.nz. Always ask to see their PGDB licence before work begins.