Yes — in most cases, gently cleaning the thermocouple on your gas heater is something a homeowner can safely do themselves, and it's one of the most common fixes for a pilot light that won't stay lit. That said, there are clear limits to what you should tackle yourself, and any work that involves disconnecting gas lines or internal components must be carried out by a licensed gasfitter registered with the Plumbers Gasfitters & Drainlayers Board (PGDB).
What Is a Thermocouple and Why Does It Matter?
A thermocouple is a small safety device found on most older gas heaters and some newer ones. It sits in the pilot flame and generates a tiny electrical current when heated. This current signals the gas valve to stay open. If the thermocouple is dirty, corroded, or faulty, it can't generate enough current — so the gas valve shuts off and your pilot won't stay lit, even after you hold the ignition button down.
This is a very common issue in New Zealand homes, particularly with older unflued gas heaters and flued gas fires that have been sitting unused over summer.
Safety First
Important: Before doing anything, turn off the gas supply at the appliance isolation valve (or at the meter if there is no isolation valve) and allow the heater to cool completely. Never work on a gas appliance while it is hot or while gas is flowing. If you ever smell gas, do not attempt any work — ventilate the area, leave the house, and call your gas supplier or 111.
For general gas safety guidance, refer to WorkSafe NZ.
What a Homeowner Can Safely Do
Cleaning the thermocouple tip is considered basic maintenance and does not require disconnecting any gas lines, so it falls outside the definition of restricted gasfitting work under the Gas Act 1992 — though if you are uncertain whether your specific situation is covered, check with the PGDB. Here's how to do it:
Tools You'll Need
- Fine steel wool or very fine-grit emery cloth (400-grit or finer)
- A soft, clean cloth
- A small screwdriver (to access the burner compartment, if needed)
Step-by-Step Cleaning Process
- Turn off the gas at the appliance valve and let the heater cool fully — at least 30 minutes.
- Locate the thermocouple. It's the thin copper or steel rod positioned so its tip sits directly in the pilot flame. Consult your heater's manual if you're unsure.
- Inspect the tip. Look for a build-up of carbon (black soot), oxidation, or corrosion on the metal tip.
- Gently clean the tip. Use fine steel wool or emery cloth to lightly rub the tip of the thermocouple until the metal looks clean and slightly shiny. Don't scrub aggressively — you only need to remove surface deposits.
- Wipe away any residue with a clean, dry cloth.
- Reassemble and test. Turn the gas back on, relight the pilot following the manufacturer's instructions, and check whether the pilot stays lit.
If the pilot still won't stay lit after cleaning, the thermocouple may be worn out and need replacing — or there could be another fault in the gas valve or ignition system.
What Is Restricted Gasfitting Work?
Under NZ law, restricted gasfitting work must only be performed by a licensed gasfitter. This includes:
- Disconnecting or reconnecting any gas pipework or fittings
- Replacing the thermocouple (if it involves disconnecting the gas line connection at the valve)
- Servicing or replacing the gas valve, burner, or regulator
- Any internal work beyond basic external cleaning
Always check with the PGDB if you're unsure whether a task is restricted. Doing restricted work yourself is illegal and can void your insurance.
Other Reasons Your Pilot Won't Stay Lit
If cleaning doesn't solve the problem, consider these other causes:
| Possible Cause | DIY Fix? | Notes |
|---|---|---|
| Worn/failed thermocouple | No — call a gasfitter | Thermocouple replacement involves gas connections |
| Blocked pilot orifice | Possibly — compressed air only | Do not use metal objects to clear it |
| Faulty gas valve | No — call a gasfitter | Restricted work |
| Draughts blowing out pilot | Yes | Reposition heater or check flue draught |
| Low gas pressure | No — call your gas supplier | Could indicate a wider supply issue |
Healthy Homes and Unflued Gas Heaters
If you're a landlord, be aware that Tenancy Services Healthy Homes standards have specific requirements around heating. Unflued gas heaters are not an acceptable primary heating source under the Healthy Homes heating standard. It's worth reviewing whether your appliance meets current requirements.
For energy efficiency and ventilation advice, Energywise is a useful NZ resource.
When to Call a Professional
Call a licensed gasfitter if:
- Cleaning the thermocouple doesn't fix the problem
- You need the thermocouple replaced
- You notice any smell of gas at any point
- The heater hasn't been professionally serviced in several years
- You're unsure about any step in the process
Gas appliances should be serviced by a licensed gasfitter every 1–2 years as a general rule, though always follow your manufacturer's recommendations. You can find qualified local gasfitters on tradedirectory.co.nz.
Certifying Plumber
