How to Relight a Gas Hot Water Pilot Light Safely (and When to Stop)

If you can smell gas, stop: turn the control to off only if you can reach it safely, get everyone outside, and call from outside. Otherwise the sequence is: turn the gas control knob to off, wait 5 minutes for gas to clear, turn it to pilot, press and hold the knob down, ignite the pilot, keep holding for 30 to 60 seconds so the thermocouple heats, then release and turn to on. If it fails twice, stop and book a licensed gas fitter.

The short version

Smell of gas, scorch marks, a damaged flue, or anyone feeling headachy or nauseous indoors: do not relight anything. Ventilate, get out, and call from outside.
Most gas hot water units installed in Adelaide since the mid 2000s are continuous flow with electronic ignition and have no standing pilot to relight.
Hold the control knob down for 30 to 60 seconds after the flame lights. You are holding a safety valve open until the thermocouple generates enough voltage to hold it itself.
Relight twice at most. A pilot that will not hold on the second attempt is a fault, not user error, and repeated attempts on a unit with a flue problem are genuinely dangerous.
A pilot that drops out on windy days is telling you about its flue cowl. A pilot that needs a longer hold each month is telling you about its thermocouple.

Need this sorted rather than explained? Hot Water in Adelaide. Also worth reading: Hot Water System Leaking? Where the Water Comes From Decides the Fix · Sacrificial Anode Replacement: How Often, and When It Is Not Worth Doing

Before you touch anything

With no gas smell, there is still a short list that means stop. Any of these turns a relight into a service call.

Water leaking from the body of the unit or pooling underneath it. A leaking tank is finished, and relighting achieves nothing.
Scorch marks, soot or heat discolouration around the burner opening, the casing or the flue outlet. That is evidence of combustion going where it should not.
A flue that is rusted through, crushed, disconnected, or missing its cowl.
Rust flakes falling out of the combustion chamber when you open the panel.
Anyone in the house with a headache, nausea or dizziness that clears outside. Treat that as carbon monoxide until proven otherwise: get everyone out and call for help.
An internal or room-sealed appliance. Those are opened by a licensed gas fitter, not by the householder.

In South Australia, gas fitting is licensed work regulated by the Office of the Technical Regulator. Following the manufacturer instructions printed on your own appliance to relight its pilot is not gas fitting, and you may do it. Removing a burner assembly, replacing a thermocouple, adjusting the gas control valve or touching the flue is gas fitting, and doing it yourself is unlawful and uninsurable.

First check that you have a pilot light at all

This is the most common wasted afternoon on the subject. Most gas hot water units installed across Adelaide since the mid 2000s are continuous flow with electronic ignition and have no standing pilot. There is nothing to relight, and no relighting guide changes that.

A standing pilot unit is a tall cylindrical storage tank with a control valve near the bottom, a knob marked OFF, PILOT and ON, and a small window at the base where you can see a flame.
A continuous flow unit is a flat rectangular box mounted on an external wall, usually with a flue outlet on top and a power lead running to a nearby outdoor socket.
The quickest test: if the unit has a power lead, it does not have a standing pilot. Electronic ignition needs power, and a standing pilot does not.

If there is no pilot and there is no hot water, the fault sits elsewhere: a tripped power point or safety switch, a failed ignition electrode or flame sensing rod, a water flow sensor not registering the tap opening, a controller fault, or the gas supply. Most continuous flow units display a numeric fault code when this happens. Write it down before you call anyone. That code tells a gas fitter which part to put in the van, and it turns 2 visits into 1.

Find the parts, and understand the part that matters

The gas isolation valve. Usually within a metre of the unit on the supply line, either a small lever or a tap with a screwdriver slot. Find it first, so you can stop the fuel quickly.
The gas control valve. The body with the OFF, PILOT and ON knob on it, sometimes with a separate red or black piezo igniter button beside it.
The access panel or cover, which comes off to expose the burner compartment.
The pilot burner. A small nozzle producing a flame no bigger than a thumbnail.
The thermocouple. A thin copper tube tipped with a small metal bead, positioned so the pilot flame wraps around the tip.
The flue and its cowl at the top of the unit.

The thermocouple is the component the whole procedure revolves around. Its tip generates a few millivolts when heated, and those millivolts hold open an electromagnetic valve inside the gas control. No flame means no millivolts, the valve closes, and the gas stops. That is a safety device working as designed: it prevents a unit with a blown-out pilot from quietly filling its burner compartment with unburnt gas.

Which is why you press and hold the knob for 30 to 60 seconds. You are overriding that valve by hand while the thermocouple gets hot enough to hold it open itself. Release too early and the valve shuts, the flame dies, and it looks like a failed relight when the sequence was cut short.

The relighting sequence, step by step

Read the instruction plate on the unit first. Manufacturers vary, and the plate on your appliance beats any general guide including this one.
Turn the gas control knob to OFF and wait a full 5 minutes with the area open to fresh air, clearing unburnt gas from the burner compartment before any flame goes near it.
Remove the access panel or open the viewing cover so you can see the pilot burner and the thermocouple tip.
Turn the control knob to PILOT, lining the mark up with the indicator.
Press the knob down and hold it. That releases gas to the pilot only.
Ignite. Press the piezo button repeatedly if the unit has one, or apply a long-reach lighter on a manual ignition model. Use a torch for light, never a flame.
Keep the knob held down for 30 to 60 seconds once the flame is alight, so the thermocouple heats fully.
Release the knob slowly. The pilot should stay burning. If it goes out, wait 5 minutes and try once more, holding longer.
Turn the knob to ON. The main burner should fire with an audible whoosh. Refit the panel and allow 20 to 40 minutes before expecting hot water at the tap.

Read the flame before you close it up

What you see	What it means	What to do
Small, steady, mostly blue, wrapping the thermocouple tip	Correct combustion	Refit the panel and carry on
Yellow or orange, lazy, flickering	Poor air mix, usually a partly blocked pilot orifice or restricted air path	Turn it off and book a gas fitter. Yellow flames produce carbon monoxide
Flame lifting off the burner, or roaring	Gas pressure or injector fault	Turn it off at the isolation valve and book a gas fitter
Blue but not actually touching the thermocouple bead	Bent or misaligned pilot assembly	Book a gas fitter. Do not bend it back yourself
Soot on the surrounds, or an exhaust smell indoors	Incomplete combustion, possible flue fault	Turn off at the isolation valve, ventilate, and call immediately

What the pilot flame is telling you

The blue-flame test is not a nicety. A correct gas flame is blue because the fuel is getting the air it needs. A yellow flame means it is burning incompletely, and incomplete combustion of natural gas produces carbon monoxide. On an external unit vented to atmosphere the risk is manageable. Indoors or in an enclosed space it is not, and that is where you stop.

It lights, then goes out again

A pilot that lights cleanly then drops out is giving you a diagnosis if you watch the pattern. These are the causes in the order they turn up on Adelaide jobs.

Spiders. Small web-building spiders colonise the warm, sheltered burner compartment of an outdoor unit and web up the pilot orifice, an opening a fraction of a millimetre across that takes almost nothing to block. This is why manufacturers supply insect screens, and it is a leading cause of a unit that has run faultlessly for years suddenly refusing to hold a pilot.
Wind. Adelaide's afternoon south-westerly hits the western and southern walls where hot water units live, and a missing, loose or corroded flue cowl lets a gust reach the pilot. A unit that goes out on windy days and behaves the rest of the time is telling you about its cowl, not its thermocouple.
A tired thermocouple. Output falls as the tip oxidises with age. The classic pattern is a pilot that burns while the knob is held, drops out around 30 seconds after release, and needs a longer hold each month until it stops holding at all.
Carbon or scale on the pilot orifice after years of running, which produces the same starved, yellow-tinged flame as a spider web.
A failing gas control valve. What is left when a new thermocouple does not fix it: the electromagnet no longer holds on the voltage a healthy thermocouple produces.
The obvious. An LPG cylinder that has run empty, or an isolation valve left closed after other work on the property. Check these before assuming a fault.

The pattern is the diagnosis. Fails only in wind points at the flue. Needs an ever-longer hold points at the thermocouple. Went out for the first time in 9 years with no change in conditions points at the burner compartment, and at something living in it.

The judgement worth making is about the age of the tank behind the fault, not the fault itself. On a gas storage unit under 8 years old, a thermocouple or a pilot clean is worth doing without hesitation, because the unit has most of its life ahead of it. On a unit at 12 years or more the arithmetic changes, because a major part is going into a tank already at the end of its service life, whose anode was consumed years ago and whose relief valve is next.

Marc is a licensed plumber and gas fitter with 20 years of experience, and he texts an arrival time before setting off instead of leaving you on a window. The price is discussed before work starts, and if a pilot clean is all your unit needs, that is what you will be charged for.

Questions we get asked

Why does my hot water pilot light keep going out?

The pattern tells you which fault it is. Going out only on windy days points to a damaged or missing flue cowl letting gusts reach the pilot. Needing a longer and longer hold on the control knob over several months points to a thermocouple that is losing output as its tip oxidises. Going out abruptly after years of trouble-free running, with no change in weather, usually means the pilot orifice is blocked, and on Adelaide outdoor units that is frequently a spider web. A pilot that will not hold even with a new thermocouple points at the gas control valve.

How long do I hold the pilot button down for?

Between 30 and 60 seconds after the flame is alight, and longer on a second attempt. Holding the knob down manually overrides a safety valve inside the gas control while the thermocouple heats up enough to generate the few millivolts that hold the valve open by itself. Release before the thermocouple is hot and the valve shuts, the flame dies, and it looks like a failed relight when the sequence was just cut short.

Am I allowed to relight my own pilot light in South Australia?

Yes. Following the manufacturer instructions printed on your own appliance to relight its pilot is not gas fitting work, and you may do it. Anything beyond that is: removing a burner assembly, replacing a thermocouple, adjusting the gas control valve, or working on the flue is licensed gas fitting work regulated by the Office of the Technical Regulator, and doing it yourself is unlawful and leaves you uninsured.

What does a yellow pilot flame mean?

It means the flame is not getting the air it needs and the gas is burning incompletely, usually because the pilot orifice is partly blocked or the air path into the burner compartment is restricted. Incomplete combustion of natural gas produces carbon monoxide. Turn the unit off and book a licensed gas fitter. A correct pilot flame is small, steady and mostly blue, and it wraps around the thermocouple tip.

My gas hot water unit has no pilot light. What do I do?

That means it is a continuous flow unit with electronic ignition, which is what most Adelaide installations since the mid 2000s are, and there is nothing to relight. Check the power point and the safety switch first, since these units need mains power to fire. Then look for a fault code on the controller or the unit and write it down. That code identifies the failed component, and giving it to a gas fitter over the phone means the right part arrives on the first visit.