Gas water heater not lighting

Introduction of the Gas water heater not lighting

A gas water heater provides hot water for your home using natural gas or propane as its fuel source. Inside the tank, a pilot light ignites the burner when hot water is needed. However, gas water heaters sometimes fail to light properly. There are several components involved in the ignition process that can malfunction and cause startup issues.

Understanding the root of the problem is key to getting your gas water heater relit. This article explores the various causes of gas water heater ignition failure and steps you can take to troubleshoot and fix them. We’ll also cover when it’s best to call a professional for repairs. Armed with the right information, you can get your water heater back up and running.

Pilot Light is Out

The small pilot light plays a crucial role in igniting the main burner inside a gas water heater. Situated near the main burner, the pilot light provides a flame to light the gas when the thermostat calls for heat. If the pilot light goes out, the burner cannot ignite.

There are two main issues that can cause a pilot light to go out. First, it may simply burn out over time. Pilot lights can go out due to dirt buildup on the ignitor or a weak flame. Second, a draft may blow out the pilot light. Vents located too close to the pilot light assembly can gust air and extinguish the flame.

Locate the ignitor button and follow the manufacturer’s instructions to light it. If it won’t stay lit, the thermocouple likely needs replacement. This inexpensive component generates voltage to hold the gas valve in the open position. A weak thermocouple cannot keep the flame going.

Installing a new thermocouple generally takes less than 30 minutes. Make sure to purchase one that is compatible with your water heater brand and model. With a functioning thermocouple, the pilot light will remain constantly lit and ready to ignite the burner.

Gas Supply Issues

Ignition failure is often caused by problems with the gas supply itself. Your gas water heater needs adequate gas flow at the right pressure to ignite properly. Any interruption in the gas supply will prevent the burner from lighting.

Start by checking that the main gas shut-off valve is fully open. This gas meter valve is typically located near gas station. Make sure it is turned on all the way to allow full gas flow.

Low gas pressure is another issue that can affect ignition. The minimum gas pressure for most residential water heaters is 7″ of water column for natural gas models. Propane models need at least 11″ of water column. Pressure below these thresholds can lead to ignition failure. A technician can diagnose and remedy inadequate gas line pressure.

The gas control valve is also essential for proper water heater operation. This device manages gas input in response to signals from the thermostat. If it is defective, gas flow will be irregular or interrupted. A new gas control valve will be required if diagnosed as faulty. Installation is complex and best left to qualified professionals.

Thermocouple Problems

Sitting just within the pilot light flame, the thermocouple generates a small electric current to hold the gas valve in the open position. This allows gas to continue flowing to the pilot light. If the thermocouple fails, the pilot light is deprived of gas and can go out.

A weak or damaged thermocouple is one of the most common causes of ignition issues in gas water heaters. Symptoms include a pilot light that won’t stay lit and repeated ignition failures. If jiggling the thermocouple temporarily helps ignite the pilot, it likely needs replacement.

Replacing a bad thermocouple is a straightforward repair. These inexpensive parts can be found at most hardware stores. Use caution when handling thermocouples, as they are fragile. Make sure the new one is fully pressed into place within the pilot light housing. This should resolve any problems keeping the pilot light on.

Ignitor or Ignition Control Failure

For the main burner to ignite, a spark must occur to light the gas. This is where the ignitor and ignition control module come in. Situated near the burner, the ignitor creates a spark when the water heater cycles on. If either component fails, the burner cannot ignite.

A faulty ignitor will simply stop sparking, while an ignition control issue prevents voltage from reaching the ignitor. To diagnose, turn up the thermostat and watch for spark activity when the pilot light is on. No spark likely indicates a problem with one or both of these components.

Replacement ignitors are inexpensive, but the ignition control is a more involved repair. A technician can determine if only the ignitor needs replacement or if the control is also faulty. Proper installation is key to prevent gas leaks or burner misfiring. Allow a professional to handle any ignition control replacements.

Flue Blockage

The flue is a vertical vent pipe that releases exhaust gases outside as the water heater operates. If the flue becomes blocked, combustion gases can spill into the room instead of properly venting. This is a dangerous situation in addition to causing ignition failure.

There are a few reasons flue blockages occur. Bird nests, leaves, and other debris are common culprits. A rusted, corroded flue can also accumulate scale that impedes airflow. Rodents sometimes nest inside vent pipes, occluding the flue entirely.

Check for obstructions by visually inspecting the top of the flue. Use caution not to dislodge or damage any parts. If you cannot see inside clearly, a technician can insert a special flue camera to identify the issue. Removing debris and clearing fully blocked flues may require a professional.

Proper maintenance is key to preventing flue blockages. Keep tree branches and shrubs trimmed away from vents. Install wire mesh screens over wall or roof terminations. Schedule annual flue inspections and cleanings to nip problems in the bud. Taking these preventive measures reduces ignition failure occurrences.

Gas water heater not lighting
Gas water heater not lighting

Water Heater Venting Problems

In addition to the flue, gas water heaters also rely on intake and exhaust venting. Combustion requires proper air intake through a dedicated vent. Exhaust gases exit via a separate vent. If either vent is blocked, restricted, or improperly installed, ignition failure results.

Check vent terminations outside to ensure they are not blocked by debris, dirt, or snow. Make sure exhaust and intake vents remain at least 12″ apart. Also verify vent piping is intact, sloped properly to allow drainage, and secured tightly with no leaks.

DIY repairs are not recommended for venting issues. The configuration is complex and precisely engineered for safety. Improper positioning or disconnects can lead to dangerous exhaust gas leakage and carbon monoxide poisoning. Therefore, a licensed professional should diagnose and remedy any venting problems.

Sediment Buildup

Over time, hard water can leave behind mineral deposits inside the tank called sediment. Excessive sediment accumulation can lead to ignition failure in a few ways. Large debris can clog gas supply lines or coat the pilot assembly. Sediment can also insulate the thermocouple and prevent proper sparking.

Draining the tank is the solution for heavy sediment buildup. Locate the tank drain valve and attach a garden hose to direct water outside or into buckets. Drain 2-3 gallons initially to purge loose sediment. If water flow remains slow, a full flush is needed to clear heavy deposits clogging intake screens.

Preventative tank flushing every 6-12 months helps avoid major sediment problems. Use a de-liming agent to dissolve minerals and flush them out. Replace old steel tanks prone to rust buildup with newer enamel or glass-lined models. With periodic flushing, sediment accumulation remains minimal.

Thermostat Issues

The thermostat controls temperature regulation. When hot water is needed, the thermostat triggers the ignition process allowing gas to flow. A faulty thermostat affects ignition in a few ways.

If the thermostat stops working entirely, it won’t initiate the ignition sequence at all. The pilot light and main burner will never receive gas flow. A worn out or defective thermostat also may not properly sense water temperature. This leads to irregular heating cycles and ignition failures.

Replacing the thermostat will restore normal ignition functionality. Identify the thermostat manufacturer and model to acquire the correct replacement part. Carefully disconnect the wiring and remove the old thermostat. Install the new unit according to the manufacturer’s specifications.

When to Call a Professional

Some ignition problems are quick fixes, but more complex repairs are best left to qualified technicians:

  • Gas leaks – Never attempt to relight a water heater with a known gas leak. Escaping gas is extremely hazardous. Call the gas company or a plumber immediately.
  • Carbon monoxide issues – Improper venting can cause carbon monoxide to spill into living spaces. Address any CO problems professionally.
  • Sediment removal on old tanks – Heavy limescale removal on aged tanks risks internal damage. Let a pro handle stubborn sediment.
  • Venting repairs – As mentioned, any issues with exhaust or intake vents should be handled by a licensed plumber.

Major component replacements – Professionals have specialized tools and expertise to safely replace control valves, burners, and other key parts.

Diagnosing the ignition problem yourself can save a service call fee. But extensive repairs requiring part replacements or venting configurations call for an expert. Combine DIY troubleshooting with professional repair when needed to get your gas water heater relit quickly and safely.


1. Why won’t my pilot light ignite?

Common reasons include a weak thermocouple, dirt buildup on the ignitor, or a problem with the gas control valve. Checking these components can help to issue identify.

2. What should I do if the pilot light repeatedly goes out?

If the pilot light won’t stay lit, it likely indicates an issue with the thermocouple not generating enough voltage to keep the gas valve open. Replacing the thermocouple often solves this problem.

3. Why does my water heater ignite sometimes but not others?

Intermittent ignition failures can be caused by a weak thermocouple, flaky gas control valve, or an ignitor that’s slowly wearing out. Testing each component can reveal the culprit.

4. I pressed the ignition button but nothing happened – now what?

If the ignitor doesn’t spark, the issue could be within the ignition control module itself. This would technician need to be replace.

5. Does sediment or rust buildup prevent a water heater from lighting?

Yes, heavy sediment buildup can block gas flow and cause ignition failure. Flushing the tank annually can help prevent this issue.


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