Why Won’t My Water Heater Light?

Why won't my water heater light?

If you have a natural gas or propane water heater and have opened your hot water faucet to find that there’s no hot water, the usual culprit is the pilot light going out. The pilot light is a small flame that ignites the gas burner. When it goes out, the first thing you should try to do is relight the water heater’s pilot, following the directions on the water heater label.

However, in some cases, other issues can prevent the pilot light from being lit.  Here are some of the reasons your water heater will not light and some troubleshooting methods:


If the pilot light does not relight, or if it goes out again right after lighting, the most common cause is a bad thermocouple. Thermocouples are an essential part of gas-powered heating appliances. If the pilot light on a unit ever goes out, gas may be released into the environment around the water heater, which creates a dangerous explosion risk and health hazard.

To prevent this occurring, appliances use a thermocouple as a fail-safe circuit to detect when the pilot light is still burning. When the pilot light remains lit, the thermocouple stays hot, and the pilot gas valve is held open. If the pilot light goes out, the thermocouple temperature falls, causing the voltage across the thermocouple to drop and the valve to close.  However, if the thermocouple is faulty, the gas valve will not open, which can prevent the pilot light from being lit. This will typically require a professional plumber to correct the problem.

Repair water heater isolated on whitePilot Tube

If there is nothing wrong with the thermocouple, then another potential cause for a heater failing to light is a dirty pilot tube. Dirt, oil, and occasionally carbon can build up and block the proper flow of gas to the burner system and pilot light. Luckily, fixing this is a pretty easy and straightforward process.

After turning the gas off and waiting a few minutes for the pilot to cool, use a needle or other thin and sturdy piece of metal to clean out the tube. You will want to scrape clean the interior surfaces of the tube and clear out any large objects that might be obstructing the tube. After a good cleaning, turn everything back on and see if the pilot will light. If it fails to ignite, then just repeat the process until everything is thoroughly cleaned.  If you cannot clean the pilot tube yourself (perhaps a lack of tools or manual dexterity) call a professional plumber to help with this.

Flex Tubing

Another possible reason why the pilot light will not stay lit can be due to the flex tubing. This tubing connects to the gas controller.  It will ensure a continuous flow of gas to the burner systems and pilot light. Sometimes, this tubing will become twisted, worn, or degraded, which will prevent proper gas flow. If the tubing has become twisted, then straightening the tube should resolve the issue. If the tube has become worn or damaged, or if straightening it does not work, then new tubing will need to be installed. You may need a plumber to assist with installing new flex tubing for your gas water heater.

Main Control Valve

In rare instances, a problem with the main control valve can cause a pilot light to go out. Gas main control valves, are generally among the last components to fail on your water heater. If the primary control valve is indeed faulty, then it will need to be replaced to fix the problem.

Troubleshooting these basic causes of a water heater that won’t light can help to restore your hot water supply and bring comfort back to your home. If these steps don’t work, or you need extra help getting to the bottom of your water heater issues, contact the professional plumbers at Magnificent Plumbing for expert advice.

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