If your gas oven flame lights up fine but goes out the moment you release the control knob, the most likely cause is a thermocouple that is either dirty, worn out, or faulty. This is one of the most common gas oven faults in NZ homes, and understanding how the safety system works will help you figure out your next step.
How the Thermocouple Safety System Works
Gas ovens are fitted with a flame failure device (FFD), and the thermocouple is the heart of it. Here's the sequence:
- You push the knob in and hold it — this manually opens the gas valve and lets gas flow to the burner.
- You ignite the burner (either with a spark igniter or a match).
- The thermocouple — a small metal probe sitting in the flame — heats up and generates a tiny electrical voltage.
- That voltage signals the gas safety valve to stay open.
- When you release the knob after holding it for long enough (usually 10–20 seconds), the valve stays open because the thermocouple is keeping it energised.
If the flame goes out when you release the knob, the thermocouple either hasn't heated up enough, isn't generating sufficient voltage, or the safety valve isn't responding to it. This is a deliberate safety feature — if the flame ever blows out accidentally, the valve closes automatically to prevent unburned gas from filling your kitchen.
Common Reasons the Flame Won't Stay Lit
1. Dirty or Sooty Thermocouple
Cooking residue, grease, and carbon build-up can coat the thermocouple tip and insulate it from the flame. This is the most common and easiest-to-fix cause.
2. Thermocouple Not Positioned in the Flame
If the thermocouple probe has shifted or bent slightly, it may not be sitting directly in the flame cone. It needs to be fully engulfed by the flame to heat up properly.
3. Worn-Out or Faulty Thermocouple
Thermocouples have a finite lifespan. Over time the internal junction degrades and it simply stops generating enough voltage to hold the valve open.
4. Faulty Gas Safety Valve
Less commonly, the electromagnetic safety valve itself can fail and won't hold open even when the thermocouple is working correctly.
5. Not Holding the Knob In Long Enough
This isn't a fault — it's operator technique. The thermocouple needs time to heat up. Try holding the knob in firmly for a full 15–20 seconds after lighting before releasing it slowly.
What a Homeowner Can Safely Do
There are a couple of things you can check and try yourself before calling a gasfitter:
- Clean the thermocouple tip. Turn the oven off and let it cool completely. Use fine steel wool or a soft abrasive cloth to gently clean any carbon or residue off the tip of the thermocouple probe. Don't bend or force it.
- Check the thermocouple position. Make sure the probe tip is sitting directly in the path of the burner flame. If it has shifted, you may be able to gently reposition it — but don't force it if it seems firmly fixed.
- Try holding the knob longer. Push the knob in firmly, light the burner, and hold for at least 15–20 seconds before slowly releasing.
If none of these steps fix the problem, the thermocouple or safety valve likely needs replacing — and that's where a licensed gasfitter comes in.
What Is Restricted Gas Work in New Zealand?
In New Zealand, gas fitting work is restricted work under the Gas Act 1992. This means that replacing components connected to the gas supply — including thermocouples, gas valves, burner assemblies, and gas connections — must be carried out by a licensed gasfitter registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB).
Attempting this work yourself is not only illegal — it can be extremely dangerous. A poorly fitted gas component can cause gas leaks, fires, or carbon monoxide poisoning.
Safety note: If you ever smell gas in your home, do not attempt to light any appliance. Ventilate the area immediately, avoid switching any electrical switches on or off, and call your gas supplier or 111 if you suspect a serious leak.
When to Call a Professional
Call a licensed gasfitter if:
- Cleaning the thermocouple and adjusting your technique doesn't fix the problem.
- The thermocouple tip looks visibly damaged, corroded, or broken.
- The oven is old and has never been serviced.
- You smell gas at any point during operation.
- You're unsure about anything to do with the gas components.
A gasfitter can test the thermocouple's output voltage with a multimeter, replace the thermocouple or safety valve if needed, and certify the work is safe. Thermocouple replacement is generally a straightforward job for a professional and shouldn't take long.
You can find qualified, local gasfitters in your area through tradedirectory.co.nz.
A Quick Comparison: DIY vs. Licensed Gasfitter
| Task | Homeowner OK? | Licensed Gasfitter Required? |
|---|---|---|
| Clean thermocouple tip | ✅ Yes | No |
| Reposition thermocouple probe | ✅ With care | Recommended |
| Replace thermocouple | ❌ No | ✅ Yes |
| Replace gas safety valve | ❌ No | ✅ Yes |
| Test gas connections | ❌ No | ✅ Yes |
Certifying Plumber
