A water heater pilot light that won’t stay lit can be a frustrating problem for any homeowner. The pilot light is a small flame that ignites the gas burner in your water heater when hot water is needed. If the pilot light goes out repeatedly, you’ll be stuck with cold showers and no hot water until you can get it relit. Here are some of the most common causes of a water heater pilot light that won’t stay lit and tips on how to fix the issue.
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1. Dirt or Debris Buildup
One of the most common reasons a pilot light won’t stay lit is because dirt, dust, spider webs, pet hair, or other debris has built up around the pilot light assembly. This prevents the pilot flame from getting enough oxygen to burn properly. A dirty or clogged pilot tube can also block the gas flow to the pilot light.
To fix this, carefully use compressed air or a pipe cleaner to clean out the pilot tube and any dirt buildup around the pilot light assembly. Use a vacuum cleaner with a hose attachment to suck up any loose debris. Make sure not to damage any of the components. After cleaning, try relighting the pilot light to see if it stays lit.
2. Weak Gas Flow
If the gas flow to the water heater is too weak, the pilot light may not get enough fuel to burn steadily. Causes of decreased gas flow include:
- Low gas line pressure – The gas lines leading to your home or water heater may not be supplying adequate pressure.
- Partially closed gas shutoff valve – Make sure the shutoff valve is turned fully open.
- Kinked/damaged gas line – Check the flex gas line and pipes for any damage or kinks that restrict flow.
- Clogged gas line – Debris in the gas line like dirt, rust, or sediment can build up over time.
- Undersized gas line – Gas lines that are too narrow can’t deliver enough gas volume.
Contact your gas utility company or a plumber to inspect your gas lines and ensure adequate gas flow if adjusting the shutoff valve doesn’t help. They can determine if your gas pressure is low or gas lines need repair.
3. Faulty Pilot Assembly
The pilot assembly consists of the pilot hood, igniter/sensor, and thermocouple. Problems with these components can cause the pilot light to go out:
- Dirty pilot hood – The pilot hood covers and protects the pilot flame. Dirt or debris on the pilot hood can block airflow and cause the flame to go out.
- Bad igniter/sensor – The igniter lights the pilot flame using an electric spark. The sensor also confirms the pilot is lit. If faulty, the pilot won’t light or the gas will shut off.
- Damaged thermocouple – The thermocouple generates a small electric current to keep the gas valve open when heated by the pilot flame. A damaged thermocouple will shut off the gas.
If cleaning the pilot hood doesn’t help, you’ll need to replace any damaged pilot assembly components like the igniter, thermocouple, or the whole pilot assembly.
4. Improper Ventilation
For the pilot light to burn properly, your water heater needs adequate air flow and ventilation. Lack of oxygen or poor ventilation causes the pilot flame to burn inefficiently or go out. Check that:
- Your water heater’s ventilation openings are not blocked. Remove any objects or debris blocking the openings.
- The water heater is installed in a properly ventilated room, not in a closet or crowded area.
- The flue vent pipe that runs from the water heater up through the roof is not blocked or damaged.
- There is enough clearance around the water heater for air circulation.
Opening a window or door near the water heater can help provide temporary ventilation. Proper ventilation and air flow are crucial for consistent pilot operation.
5. Thermostat or Safety Issues
Problems with the thermostat or safety mechanisms in a water heater can also cause pilot light issues:
- Bad thermostat – If the thermostat is stuck closed, it won’t signal for the pilot light to ignite even if more hot water is needed.
- Flame sensor rod – This safety rod shuts off gas if the pilot flame goes out. Bending or damage can cause faulty shutdowns.
- Thermopile – The thermopile sends voltage signals to the gas control valve based on pilot flame heat. If it malfunctions, the pilot may go out.
- Magnesium corrosion – Corrosion buildup on the rod can cause the pilot flame to burn poorly or go out.
Replacing a damaged thermostat, thermopile, or magnesium rod may be needed to allow consistent pilot operation. Also make sure all control circuit wiring is intact with no loose or damaged connections.
6. Wind or Drafts
Strong drafts or wind around the water heater can blow out the pilot light flame. Pilot lights are delicate and even a small breeze across the pilot can cause it to go out. Sources of drafts include:
- Leaky chimneys or flues – Can create backdrafts that pull air down from the chimney.
- Window fans, ceiling fans, and room fans – Keep them off or directed away from the water heater.
- Open windows or doors near the water heater – Close them to isolate from wind drafts.
- Central HVAC return air vents – Avoid locating near the water heater.
- Kitchen or bathroom exhaust fans – Turn bath fans off when relighting the pilot.
Blocking or redirecting drafts and air currents can help prevent an unstable pilot flame. Also using a wind-resistant pilot assembly can improve reliability.
7. Flammable Vapors Nearby
Flammable substances like gasoline, paint thinners, or solvents can disrupt proper pilot operation when stored or used near the water heater. Even small amounts of flammable vapors can destabilize the pilot or cause combustion problems.
Never use or store flammable chemicals near your gas water heater. The pilot flame could ignite the vapors or may burn poorly. Remove any combustible materials from the vicinity for a consistently burning pilot light.
8. Incorrect Pilot Flame
If the pilot flame is set incorrectly, it may not burn properly or provide enough heat to activate the thermocouple. The pilot flame size should envelop 3/8″ to 1/2″ of the thermocouple’s tip according to most manufacturers’ specifications. Blue flames with yellow tips indicate proper gas combustion.
Refer to your water heater manual for the proper pilot flame adjustment. Turning the gas valve adjustment screw can raise or lower the flame height as needed for a stable pilot.
9. Thermocouple Problems
The thermocouple generates a small electrical current when heated by the pilot flame. This current signals the gas valve to stay open. Thermocouple problems that can cause pilot issues include:
- Loose thermocouple connection at the gas valve – This can interrupt the electrical signal.
- Corroded thermocouple junction – Where the thermocouple attaches at the pilot assembly. This disrupts the millivolt signal.
- Old, worn out thermocouple – Thermocouples degrade over time and need replacement.
- Wrong replacement thermocouple – Make sure new thermocouples match the original part number/spec.
- Insufficient pilot flame heat – The flame may be too small or blowing incorrectly on the thermocouple.
Carefully inspect the thermocouple and connections. Replace damaged thermocouples. Make sure the pilot flame envelops the end of the thermocouple properly so it can generate sufficient voltage to hold the gas valve open.
10. Moisture Buildup Inside
Small amounts of moisture or condensation can build up naturally inside a water heater’s sealed combustion chamber. Excess moisture on the main burner or pilot assembly can affect combustion and cause the pilot flame to go out.
To prevent this, make sure your water heater’s environment is dry, the flue pipes are pitched up so condensate drains properly, and all joints are airtight. Have your water heater serviced to clean out any moisture if needed.
Conclusion
Repeatedly relighting a pilot light that won’t stay lit can be very frustrating for homeowners. In most cases, the underlying cause is one of the issues above that prevent the pilot flame from burning properly. Thorough inspection and cleaning of the pilot assembly and related components is usually the first step in diagnosing the problem. Replacement of worn parts may be needed. Or the issue could be due to improper gas supply, poor ventilation or drafts in the room. Calling a professional for service may be needed if you can’t resolve the issue yourself using the tips above. With the right diagnosis and fix, your water heater’s pilot light can once again provide reliable operation.