How to Ignite a Gas Water Heater: Lighting and Relighting Tips

Gas water heater

Detail instructions on how properly to ignite a gas water heater. See what types of ignition systems are available with pros and cons. Tips on how to relight a water heater if the pilot light goes out and what causes it. Common problems when igniting a gas unit.

Note: Do not try to light/relight a water heater if you smell gas. Leave a house and contact your gas supplier immediately. If you have issues with your unit, it is recommended to contact a plumber.

How to ignite a gas water heater: Things to consider

A gas water heater is an integral part of most homes in North America, heating water with natural or propane gas. They last over 10 years and come with warranties from 6 to 12 years. Over their lifespan, they can develop various problems. Some of these problems are easy to fix, especially for DIY-ers, while others, more complicated, require professional assistance.

While gas models share many elements with the electric variant, gas models are more complex and require more than basic knowledge and skills to service and troubleshoot.

Every gas-powered unit is equipped with a gas control valve that combines a gas valve, a thermostat, and an ignition system.

Gas valves are in charge of releasing gas into the combustion chamber when the thermostat calls for water heating. Water heaters use several types of ignition devices so users can manually or automatically light the burner:

• Standing pilot and piezoelectric igniter (piezo)
• Hot surface igniter
• Manual ignition system

How to ignite a gas water heater: Standing pilots and piezo igniters

The standing pilot or simply pilot light was the standard ignition type for many years (and it is still popular). The pilot light generates the small burning flame that is used to light the main gas burner. It works together with the thermocouple, which must be in contact with the flame all the time.

The thermocouple senses the heat, which creates a small electrical current. This is enough electricity to keep the gas valve open to deliver gas to the pilot light. For the water heater to operate correctly, the pilot flame must be ON, continually. The gas valve closes if the thermocouple doesn't register the flame.

Piezo igniters are designed to generate electric sparks and ignite the gas. Standard piezo igniters found in today's water heaters are push-button type and are built into the gas control valve. They do not require an electrical connection to operate.

How to ignite a gas water heater: Hot surface igniters

Gas water heaters can also use hot surface igniters (HSI), resistance elements that are made of silicon carbide or silicon nitride. When a specific voltage is applied to the HSI, it starts glowing (orange to red, lighting the gas with the generated heat.

Today, most models are equipped with pilot lights and piezo igniters, while advanced models utilize hot surface igniters. Some older models do not have igniter buttons (you have to use a long matchstick or a BBQ lighter), which are considered manual.

Note: In some models, when a call for heating is initiated, an ignition system will try to light the burner several times. If the control panel doesn't detect ignition, a water heater locks out, flashing the corresponding error code.

Every gas device has a label with instructions on how to light a water heater attached.

Use it.

Of course, there must be an unobstructed gas flow from the supplier and the main shut-off valve open.

Make sure that the tank is filled with water before turning ON the unit.

Instructions on how to ignite a water heater using a pilot light and piezo ignition

• Locate a gas control valve found at the bottom of the unit. This is a command center where you light a pilot, turn ON or OFF gas supply to a water heater, and where you would change the temperature.
• Remove the metal cover plate to get access to a viewport and where you can visually check the status of a pilot and a burner flame.
• If your heater was previously working, it is recommended to turn the gas OFF and let it sit for 5 minutes so any excess gas inside the gas chamber can disappear.
• Turn the thermostat to its lowest position.
• Turn the gas control knob to the "pilot" position.
• Press the knob and hold it down. At the same time, press a separate ignition button to ignite the standing pilot. It will repeatedly click, generating a spark. The electric spark will light the pilot.
• Once the pilot is ON, keep the knob pressed for 30 seconds and then release it slowly. It pops back up. Some models have a status light that blinks when the pilot is lit. The pilot should now burn steadily. If not, repeat the procedure but keep the gas control knob pressed longer. This will allow the pilot flame to heat the thermocouple. Once it detects the flame, the gas valve opens.
• With the standing pilot burning, turn the gas knob to the ON position to light the main gas burner inside the water heater. You will hear a distinct "whooshing" and "whoomp" sound as the gas burner ignites.
• Set the thermostat to the temperature you want it (the recommendation is around 120 F).
• Put the cover plate back.

How to light a gas burner if a water heater is equipped with the hot surface igniter (HSI)

• Turn OFF the electrical supply to the water heater.
• Turn the thermostat to its lowest position.
• Press the switch to the OFF position.
• Wait for 5 minutes to clear out any gas. It is safe to continue if gas is not leaking.
• Turn ON the electrical supply to the device.
• Press the switch to the ON position.
• Turn the thermostat to desired temperature (recommended temperature: 120-125 F).

Note: The above instructions refer to a gas water heater equipped with the Honeywell gas control valve. The procedure might be similar for a model with different gas control valve types.

Instructions on how to manually ignite a water heater

• Locate the gas control valve found at the bottom of your water heater.
• Remove the metal cover and access (inner) plates. You will now have access to the gas combustion chamber with the pilot assembly and the gas burner.
• If the unit was previously working, turn the gas OFF and wait for 5 minutes until there is no gas inside the unit.
• Turn the thermostat to its lowest position.
• Turn the gas control knob to the "pilot" position.
• Push the ON/OFF knob down. Use a flashlight to find the pilot. While pressing the knob down, bring a BBQ lighter close to the standing pilot assembly and light the pilot. Keep pressing the gas control knob for 30-60 seconds, or until the thermocouple gets heated enough to keep the gas valve in the ON position.
• The pilot should be lit now. If not, repeat the procedure but keep the gas control knob pressed longer. This will allow the pilot flame to heat the thermocouple so it can detect the flame.
• With the standing pilot ON, turn the gas knob to the ON position to light the main gas burner inside the water heater.
• Set the thermostat to the temperature you want it (the recommendation is around 120 F).
• Put all the cover plates back.

Note: If you couldn't light the standing pilot from the first try, repeat the process, but be careful as you don't want to release too much gas inside the combustion chamber and get unexpected results.

In the case of power vented water heaters, when the thermostat is satisfied, the burner shuts OFF while the blower keeps running for some time in the post purge mode. The unit stays in standby mode until the next call for heating.

Is it safe to relight a pilot if it goes out?

If your water heater pilot light goes out, it won't be heating water, and you would miss a nice, long hot shower.

The procedure of relighting a pilot light is the same as explained in the text above.

Relighting a pilot is fast and easy, and as long as you don't smell the gas, it is safe. If you do smell it, leave a house and contact your gas supplier immediately.

Also, if it happens frequently, call a technician.

There are many reasons why a pilot light goes out, and here are some of the reasons:

• Not enough combustible air
• Dirty thermocouple
• Dirty pilot orifice
• Damaged, dislocated, or a faulty thermocouple
• Flame blown out (draft or downdraft, for example)

If the standing pilot goes out frequently, you might want to check this article and these troubleshooting tips.

Keep in mind that when dealing with gas, it is always recommended to contact a PRO.

Proper maintenance is important to have all elements in good working condition and the water heater running with no interruptions. Check the main burner and ignition system at least once a year. Clean the debris and soot if needed, so as any deposits on the igniter/flame rods.