How to Turn On a Gas Hot Water System

Need hot water back on fast? Here’s exactly how to turn a gas hot water unit back on, whether you’ve got a storage tank with a pilot light or a continuous-flow (instantaneous) system. Start with safety, then follow the steps for your unit type.

The 60‑second answer

Identify your unit type first:

• Storage tank (with pilot light): You’ll see a cylinder with a small access window near the bottom and a control knob with Off–Pilot–On. Turn the gas control to Pilot, hold it down, press the igniter until the pilot lights, keep holding 30–60 seconds, then turn to On and set the temperature. Give it 30–60 minutes to reheat.
• Continuous-flow (instantaneous): A wall-mounted box with no big tank. Make sure the gas isolation and cold-water inlet valves are open, and the unit has power (240 V or batteries). Turn on a hot tap fully; the burner should fire and the display (if fitted) should show a temperature.

Safety first: If you smell gas, hear hissing, or the smell gets stronger near the unit, do not light anything. Turn off gas at the meter, ventilate, and call a licensed gasfitter or your gas distributor’s emergency line.

Before you start: quick safety and checks

• Confirm the energy type: You’re working on a gas system (natural gas or LPG). If you have solar hot water with a gas booster, you’ll be relighting the booster only.
• Sniff test: No gas smell. If there is a smell, stop and get a pro.
• Gas meter/valve on: At the meter or LPG cylinder, the handle should be in line with the pipe (on). At the unit, the small gas isolation valve should also be open (handle in line with pipe).
• Water on: The cold-water inlet valve to the unit (often a blue handle near the tank base or under a continuous-flow unit) should be fully open (anticlockwise).
• Power on (for continuous flow and some modern tanks): Ensure the powerpoint is on, circuit breaker is not tripped, and any batteries (often D-cells in older instant units) are fresh and correctly inserted.
• Ventilation: Don’t block the flue or cover panels. Keep combustibles clear of the burner area.

Storage tank: relight the pilot and turn it on

This is the classic cylinder with a burner at the bottom. The control usually has Off–Pilot–On plus a temperature dial.

Step-by-step

1. Remove the access panel near the bottom to expose the pilot view window and controls.
2. Turn the gas control to Off and wait 5 minutes to clear any gas. Keep your face back from the opening.
3. Turn to Pilot. Press and hold the control knob down to start gas flow to the pilot.
4. Ignite the pilot. Press the piezo igniter button repeatedly (you’ll hear clicks) while continuing to hold the control knob down. Watch for a small blue flame in the viewing window. If there’s no igniter, carefully use a long BBQ lighter at the pilot head while holding the knob down.
5. Keep holding 30–60 seconds after the flame appears. This heats the thermocouple/sensor so the pilot stays lit. If you release too soon, it will go out.
6. Release and check: The pilot should stay on. If it goes out, repeat once or twice, holding the knob longer. Persistent failure? See the troubleshooting checklist below.
7. Turn the control to On. Set the temperature dial to your normal setting. For storage tanks, the water in the tank must reach 60 °C to inhibit Legionella. A tempering valve mixes it down to about 50 °C for bathroom taps, as required by law.
8. Refit the access cover and allow 30–60 minutes for the burner to heat the tank (longer if the tank was stone-cold).
9. Test a hot tap. Let it run for a minute. Initial spurts and crackles are normal as air clears and the tank warms.

If the burner doesn’t fire (you can usually hear a soft roar), recheck that the gas isolation valve at the unit and at the meter are on, and that the thermostat isn’t set to “Pilot” or a low setting.

Continuous-flow (instantaneous): get it firing

Continuous-flow units heat water only when you open a hot tap. There’s no pilot light; ignition is electric (mains power or batteries). Many have a small display or temperature controller inside the home.

Step-by-step

1. Open the gas and water isolation valves at the unit (handles in line with their pipes).
2. Confirm power: The powerpoint is on and the cord is plugged in. If your unit uses batteries, fit fresh ones with correct polarity and reclose the compartment.
3. Set the temperature controller (if fitted) to your usual setting, commonly 50–55 °C for bathrooms.
4. Open a hot tap fully for 30–60 seconds. You should hear the unit click and the burner ignite. Warm water should arrive after a short delay.
5. Check for error codes: If the display shows a fault code or a status light flashes, note it for a technician.

No display? Some units only wake when flow starts. If still dead, try another power point, check the circuit breaker, and ensure the outdoor power point hasn’t tripped its safety switch.

If it won’t stay on: troubleshooting checklist

Work through these from most likely to less likely. Stop if you smell gas or see soot, scorching or melted parts — call a licensed gasfitter.

1. Gas supply off or low — Check the meter valve or LPG cylinder. For LPG, confirm there’s gas in the bottle and the changeover is set to a full cylinder.
2. Air in the gas line (after an outage or bottle change) — For storage tanks, hold the pilot knob down longer (up to 90 seconds) while sparking. For continuous flow, run a hot tap for a minute and try again.
3. Thermocouple or flame sensor issue — If a storage tank pilot lights but won’t stay on after several solid attempts, the thermocouple may be faulty or not positioned correctly. This is a job for a gasfitter.
4. Power/batteries — Instant units need power to spark and control. Replace batteries, check the outdoor GPO switch, RCD, or breaker.
5. Water flow too low — Instant units won’t fire if flow is restricted. Fully open the hot tap, check other taps, clean the inlet filter at the unit (if there’s an easy service cap), and make sure the cold inlet valve is fully open.
6. Wind or flue issues — Strong gusts can blow out a pilot or cause ignition failures. Ensure the flue terminal isn’t blocked by debris or a cover. Don’t modify flues; seek a pro if you suspect a problem.
7. Error code displayed — Note the code and reset if your model allows. If the fault returns, book a service.
8. Mixed temperature only warm — A faulty tempering valve or recirculation setup can deliver lukewarm water even if the heater is hot. Feel the hot outlet at the tank (carefully). If it’s hot but taps are warm, ask a plumber to test the tempering valve.
9. Solar booster off — For solar-gas systems, make sure the booster is enabled for cloudy weather. Check any booster switch/controller near the switchboard or hot water unit.

Settings, reheating time and safety

• Target temperatures: Storage tanks must reach 60 °C in the cylinder to control bacteria. Bathroom delivery is limited to about 50 °C via a tempering valve. Kitchen/laundry taps may be hotter.
• Reheat time: After turning a gas storage tank back on, expect 30–60 minutes for usable hot water, depending on tank size and how cold the water is. Instantaneous units provide hot water within seconds once ignited.
• Energy saving: For continuous-flow, choose the lowest comfortable setpoint (often 50–55 °C) so you’re not mixing in lots of cold water.
• Annual servicing: Have a licensed plumber/gasfitter service gas hot water every 1–2 years (instant) or 2–3 years (storage). They’ll check the burner, flue, gas pressures, anode (for enamel tanks), and the tempering valve.

When to call a licensed gasfitter

Get a professional involved if any of the following apply:

• You can smell gas that doesn’t dissipate quickly.
• The pilot won’t stay lit after several careful attempts, or the flame is large, yellow, or sooty.
• The burner goes out repeatedly or the unit trips with error codes.
• There’s scorching, melted plastic, or signs of heat damage around the burner or flue.
• Water leaks at the tank, relief valve, or pipe connections.
• You’re unsure about any step. Gas work beyond basic lighting is licensed work in Australia.

Knowing how to turn hot water system on safely can save a chilly night, but don’t push through if something doesn’t look or smell right. Gas appliances are safe when maintained and used correctly; when in doubt, call a pro.