CO alarm going off
If your CO detector is sounding, this is the page. Get out first.
Safety warning · Stop using the heater
Yellow flame on your gas heater? Turn it off now.
A healthy gas flame burns crisp blue. Yellow, orange or lazy red flames mean incomplete combustion — and incomplete combustion makes carbon monoxide (CO). CO is colourless, odourless, and the leading cause of accidental gas-poisoning deaths in Australia. Don't keep using the heater until a licensed gas fitter has done a CO safety test.
Digital CO meter on every job
Same-day Adelaide metro
Licensed gas fitter
Compliance certificate
CO risk
Should be blue
Test included
What's happening
Why a blue flame matters
Natural gas and LPG burn cleanly only when they're mixed with the right amount of air. The blue colour you see in a healthy burner is the signature of complete combustion — gas plus oxygen producing carbon dioxide and water vapour, both of which the flue safely vents outside. There's almost no carbon monoxide at all.
Yellow comes from soot particles glowing in the flame. Soot forms when the gas can't get enough oxygen to burn fully, and the unburnt carbon produces carbon monoxide instead of carbon dioxide. CO is the dangerous one. It binds to your blood 200 times stronger than oxygen, and you can't see it, smell it, or taste it. The first symptoms — headache, dizziness, nausea — are easy to mistake for a winter cold.
So a yellow flame isn't a cosmetic issue. It's the heater telling you, visibly, that something is choking the combustion. Could be a fixable nuisance like a dust-blocked air intake. Could be a serious crack in the heat exchanger. The only way to know is to measure CO at the burner with a calibrated meter — which is what we do on every callout.
Safety check
Is this dangerous?
Yes — treat it as serious. Yellow flame is one of the three major CO warning signs along with sooty marks around the flue and people in the house getting headaches when the heater runs. Most yellow-flame faults won't kill you in the next hour. But every additional day of running it is more CO into the rooms you sleep in.
People most at risk: babies, pregnant women, elderly, anyone with heart or lung issues. CO poisoning at lower levels causes long-term cognitive damage that doesn't fully reverse. This isn't fearmongering — Australian coroners' reports list CO poisoning from gas heaters every winter.
Get out and call 000 immediately if anyone in the house has: headache, dizziness, nausea, drowsiness, confusion, chest pain, or shortness of breath while the heater is running. Then ring us once everyone is safe and out of the house.
Right now
What to do in the next 5 minutes
1
Turn the heater OFF
Off at the unit and at the wall. Don't use it again until a licensed fitter has tested it.
2
Open windows
Ventilate the rooms the heater was running in. Fresh air clears any built-up CO quickly.
3
Check on the family
Anyone with headache, nausea, dizziness or drowsiness — get them outside, ring 000.
Diagnosis
What's likely causing it
- Dirty burner ports. Years of dust and lint coat the burner ports and disrupt the gas/air mix. Most common cause we see in Adelaide. Cleared with a proper burner clean and pressure test.
- Spider webs in the venturi. Sounds odd but it's the second most common culprit, especially on heaters that sat unused over summer. Spiders love the smell of the additive in natural gas. Webs choke the air intake and the flame goes yellow.
- Blocked flue or chimney. Bird nests, leaves, even paint or render from a recent reno. Combustion gases can't escape, oxygen can't get in properly, flame goes yellow. Outdoor inspection of the flue cowl is part of every service.
- Wrong gas pressure. Manifold pressure too high or too low throws off the air/gas ratio. We measure it with a manometer against the manufacturer's plate spec.
- Cracked heat exchanger. The serious one. A crack lets combustion air leak into the burner space, disrupting the mix and pushing CO straight into the house air. Heat exchanger replacement is rarely economic — usually means new heater. We'll tell you straight whether it's worth doing.
DIY?
Can I fix it myself?
Absolutely not. A yellow flame means a CO problem and CO problems are not for DIY — full stop. Even cleaning the burner properly requires the gas line disconnected and reconnected, gas pressure tested, and CO levels measured with a calibrated meter to confirm it's safe. All gas-side work in South Australia is restricted to licensed gas fitters under the Plumbing, Gas and Electrical Services Act 1995.
What you can do safely: turn the heater off, ventilate the room, and ring us. That's it.
When to call
Call us today if any of these are true
- The flame is yellow, orange, or lazy red anywhere on the burner
- You can see soot or black streaks on the heater casing or wall above
- The heater hasn't been serviced in 2+ years
- Anyone in the house has had headaches, nausea, or unusual tiredness when the heater runs
- You can smell gas at any point — call 1800 427 532 first, then us
Honest pricing
How much will the repair cost?
2026 Adelaide pricing, GST included, no call-out fee. Diagnostic and CO test are part of the service price — you're not paying extra to find the cause.
- Standard service + burner clean: $149 (wall heater), $199 (ducted)
- Burner deep clean + pressure adjustment: $220–$280
- Flue de-block: $180–$260 depending on access
- Heat exchanger replacement: $1,400+ — usually not economic on heaters over 12 years old
- Heater replacement: from $2,400 (wall) or $4,200 (ducted) — quoted separately
If we find a cracked heat exchanger we'll show you the crack on a photo or borescope and explain whether to repair or replace. No upsells.
Response time
How quickly can you come out?
Same day across Adelaide metro for yellow-flame and CO safety calls. We treat these as priority because they're a real safety issue. Ring before 10am and we'll usually be there that afternoon. After-hours and weekends, ring our emergency number — yellow flame counts as an emergency at our end.
On site, the safety test takes about 20 minutes. The repair (if it's a clean) is another 30–45. You're back to a safe, warm house in a couple of hours.
FAQ
Yellow flame — common questions
Yes. It means incomplete combustion, which produces carbon monoxide — a colourless, odourless gas that can kill. Stop using the heater and call a licensed gas fitter for a CO safety test before using again.
Crisp blue, possibly with a small yellow tip at the very top. Most of the burner pattern should be blue. Lazy yellow, orange, or red is a warning sign.
Common causes: dirty burner ports, spider webs in the venturi air intake, blocked flue, dust on the heat exchanger, wrong gas pressure, or a cracked heat exchanger. All require a licensed gas fitter to diagnose.
If the cause is a dirty burner or blocked venturi, the standard $149 service usually fixes it. Heat exchanger crack is more serious — usually means the heater is end of life and needs replacement.
Same-day across Adelaide metro for safety calls. Digital CO meters and pressure gauges in every van. If we find unsafe CO levels, we shut the heater down and red-tag it on the spot.
Related help
Other gas heater problems we help with
Banging or booming noise
Delayed ignition cracks heat exchangers. Don't keep running it.
Carbon monoxide safety guide
Why CO from gas heaters kills Australians every winter — and how to prevent it.
Yellow flame? Don't wait — book a CO safety check today.
Same-day across Adelaide metro. Digital CO meter on every job. Licensed gas fitter, fully insured.