Gas hot water pilot light won't stay lit: causes and fixes

What the pilot light and thermocouple actually do

The pilot light is a small standing flame that fires up the main burner whenever you call for hot water. Right beside it sits the thermocouple, a thin metal probe that the pilot flame keeps hot. While it stays hot, the thermocouple produces a tiny electrical current that tells the gas valve the pilot is lit and it's safe to let gas through. The instant that probe cools, the current stops and the valve shuts the gas off. That is a safety feature working exactly as designed, not a fault. So when a pilot lights and then dies the second you release the button, the system thinks the flame is out and is protecting you.

The most common cause: a worn thermocouple

Across 40 years on Western Sydney hot water units, Terry has found a worn or failed thermocouple behind the majority of "won't stay lit" callouts. Years of heating and cooling corrode the probe tip or weaken its connection, so it can no longer make enough current to hold the valve open. It's a cheap part and a straightforward swap for a licensed gas fitter, and most of these repairs land in the rough $150 to $450 range depending on the unit. If your system is 10 to 12 years old and the pilot won't hold, a new thermocouple is usually the first thing Terry checks.

Does your unit even have a pilot?

Worth a quick sanity check before you go looking for a flame. Plenty of modern continuous flow units, like the Rinnai Infinity range and newer Rheem and Bosch models, use electronic ignition and have no standing pilot at all. If yours is one of those and it's showing an error code on the controller rather than a dying pilot, that's an ignition or flame-sensing fault, not a thermocouple. It's still gas work, but the code helps a gas fitter zero in fast, so jot it down before you call.

Other reasons a pilot won't hold

• A dirty pilot or blocked orifice: dust, spider webs or corrosion can starve the pilot of gas, leaving a weak yellow flame instead of a crisp blue one. A weak flame can't heat the thermocouple properly.
• A draught: an exposed outdoor unit, a missing cover, or a gust down the flue can blow the pilot straight out.
• Gas supply issues: an empty LPG bottle, a half-turned isolation valve, or a supply problem elsewhere in the home can leave the pilot short of gas.
• A failing gas valve: less common, but a worn gas control valve won't hold the pilot even with a healthy thermocouple. That's a bigger job for a licensed gas fitter to confirm.

When to call a licensed gas fitter

You can safely try relighting the pilot once, following the printed instructions on the front of the unit (the steps below walk through it). If it won't catch, or it lights and dies straight away after a proper attempt, stop there. Gas work is not a DIY job. Dismantling a burner, replacing a thermocouple, or touching the gas valve must be done by a licensed gas fitter, both for your safety and to keep the unit compliant. Terry is a licensed plumber and gas fitter (NSW L10959) and has been sorting hot water across Berala, Lidcombe, Auburn and the wider area since 1986. If you ever smell gas, don't touch the unit, and read the safety note in the steps.

If your pilot keeps dropping out and you're tired of cold showers, give Terry a call on 0415 274 542. He quotes a fixed price before any work starts. No call centre, no subbies.