10 Signs Your Gas Heater Needs Repair (Adelaide Guide)

Published 23 April 2026 · Written by Sidney — Licensed Gas Fitter, Pilot Gas Adelaide · 9 min read

TL;DR: The top warning signs a gas heater needs repair are yellow or orange flames, sooty marks, rotten-egg or burning smells, banging on ignition, weak airflow, and your CO alarm going off. If you spot any of these, turn the heater off and ring a licensed gas fitter before you use it again.

A gas heater usually tells you it's in trouble before it dies. The problem is most people hear the warning, shrug, and keep using it until something serious happens. After 12 years servicing Adelaide homes, I can tell you the "she'll be right" approach is how we end up doing emergency calls on the coldest nights of the year — or worse, being the ones who explain to a family why a cracked heat exchanger put them in hospital.

Here are the ten signs we wish every homeowner knew to watch for.

Why these signs matter

Unlike an electric heater, a gas heater is a small controlled combustion device sitting inside your house. When it's running clean, it's safe and efficient. When something goes wrong, it produces carbon monoxide, soot, or raw gas — all of which belong outside, not inside.

Most of the signs below are early symptoms of common, fixable faults. Catch them early and a repair is a few hundred dollars. Ignore them and you're looking at a new heater — or a trip to the Royal Adelaide.

Safety warning: If you smell gas (rotten eggs) or your CO alarm is sounding, turn off the heater at the isolation valve, open windows, leave the house, and ring the emergency gas line on 1800 427 532 before ringing us.

1. The flame is yellow or orange instead of blue

A healthy gas flame burns crisp blue with maybe a small yellow tip. If you've got a window on the burner and it's burning lazy yellow or orange, that's incomplete combustion — and incomplete combustion makes carbon monoxide.

Causes: dirty burner, dust-blocked air intake, cracked heat exchanger, or a gas pressure issue. All need a fitter.

This is the number-one sign to stop using the heater and book a service. It's also one of the easiest to spot — torch the burner window next time it's running.

2. Sooty marks or black streaks around the unit

Black soot on the heater casing, around the flue, on the wall above a wall furnace, or on the floor under a space heater means combustion is dirty. Again — incomplete combustion, carbon monoxide risk.

Common on older Vulcan and Pyrox wall furnaces that haven't been serviced in years. Also common on Rinnai Energysavers with blocked flue baffles.

3. Strange smells

Three smells matter:

• Rotten egg / sulphur = raw gas leak. Turn it off, ventilate, ring the emergency gas line (1800 427 532).
• Burning dust on first use of the season is normal for the first 10 minutes. After that, it means dust is baking on the heat exchanger and needs cleaning.
• Acrid, chemical, or "hot electrical" smell = overheating components or melting insulation. Shut it off.

4. Banging or booming on startup

A bang when the heater lights is called delayed ignition. Gas is pooling in the combustion chamber before the spark catches, then all igniting at once.

Causes: dirty pilot, weak ignition electrode, gas pressure problems, or — on older ducted units — a failing gas valve.

Delayed ignition is hard on the heat exchanger. Cracks start small, then spread. Fix it fast.

5. Weak or uneven airflow

If your ducted system used to shift warm air hard and now it's a gentle breeze, you've got one of three issues: blocked return air filter, failing fan motor, or collapsed duct.

Check the return air grille first — vacuum it, check if any filter behind it needs cleaning. If airflow is still weak, it's a service call. Fan motors seize from bearing wear, and a motor that's about to fail usually screams (high-pitched) or hums (overheated winding) before it goes.

6. Short cycling — turns on and off too quickly

Healthy heaters run for several minutes, heat the room to thermostat setpoint, then cut out for a longer period. If yours fires up, runs 30–60 seconds, cuts out, then fires up again a minute later, something's wrong.

Usual culprits: failing thermostat, blocked heat exchanger causing overheat cut-out, flame sensor coated in carbon, or a faulty control board.

Short cycling isn't just annoying — it eats gas and wrecks the ignition components from the constant on/off wear.

7. Your gas bill jumped for no reason

If the heater is the only thing that's changed and your winter gas bill is noticeably up, the unit's efficiency has dropped. Dirty burners, blocked heat exchangers and slipping fan motors all force the heater to run longer for the same heat output.

A service usually restores 10–20% of lost efficiency. That often covers the cost in one winter.

8. Pilot light keeps going out

On older units with standing pilots (pre-2015 mostly), a pilot that won't stay lit points to a failing thermocouple, dirty pilot orifice, or — worst case — a gas valve on its way out.

A thermocouple is usually a $120 job. A gas valve is more like $400–$600. Book a fitter before you keep relighting it five times a night.

9. Headaches, nausea, or drowsiness when the heater runs

Safety warning: If anyone in the house gets headaches, nausea, dizziness or unusual tiredness when the heater is running — and the symptoms ease when they go outside — treat it as carbon monoxide poisoning until proven otherwise.

Turn the heater off. Open windows. Leave the house. Get medical advice. Then ring a fitter to inspect the heat exchanger and flue. Do not use the heater again until it's been cleared. Full detail is in our carbon monoxide safety guide.

10. Visible rust, cracks or damage

Inspect the outside of the heater once a year. Look for:

• Rust streaks on the casing (points to condensation inside — usually a flue issue)
• Cracks or scorch marks on the heat exchanger panel
• Loose or damaged flue pipe outside
• Bird nests, cobwebs or debris in the flue cowl
• Corroded gas line or fittings at the isolation valve

Any of these mean book a service. A damaged flue is as dangerous as a cracked heat exchanger — the whole point is to carry combustion products outside your home.

What to do if you spot one

Simple decision tree:

• Gas smell or CO alarm sounding: Turn off, ventilate, leave, call emergency gas line 1800 427 532.
• Symptoms in people: Turn off, ventilate, seek medical advice, call a fitter before re-use.
• Yellow flame, soot, banging, or weird smells: Turn off, book a fitter this week.
• Weak airflow, short cycling, higher bills: Book a service in the next fortnight.
• Visible rust or damage: Book a service before next use.

If your heater hasn't been serviced in the last two years and you're seeing any of these signs, it's overdue — see our service frequency guide for the full picture, or book a heater repair with us directly.

Typical repair cost ranges in Adelaide

Knowing rough costs helps you decide whether to repair or replace. 2026 Adelaide prices, parts and labour:

• Thermocouple replacement: $90–$150
• Ignition electrode: $110–$180
• Flame sensor clean or replace: $45–$140
• Pilot assembly rebuild: $160–$240
• Gas valve: $380–$650
• Fan motor: $420–$780
• Control board: $480–$950
• Heat exchanger replacement: $1,400+ — usually not economic
• Full unit replacement (ducted): $3,800–$11,000

Rough rule: if the repair cost is over 40% of replacement value and the unit is 12+ years old, replace it. Under 10 years old, almost always repair. Full cost breakdown in our service cost guide.

When these signs are NOT an emergency

Not every noise or smell means disaster. Don't panic-call if:

• Burning dust smell in first 10 minutes of the season. Normal. Let it run with a window open.
• Clicking before ignition. Electronic ignition electrodes click as they spark. Normal — unless it's still clicking after 30 seconds without flame.
• Gentle whoosh from ducted vents. That's the airflow doing its job.
• Small puff of steam from flue on cold morning. Condensation burning off. Normal. Thick smoke is not.
• Heater cycling every 15–25 minutes in mild weather. Normal thermostat behaviour. Short-cycling is under 2 minutes per cycle.