A gas water heater pilot light that won't stay lit is usually caused by a dirty, bent, or faulty thermocouple (or thermopile). This sensor sits in the flame and signals the gas valve to stay open; if it can't detect heat due to soot or misalignment, it shuts off the gas.
If your water heater pilot won't stay lit, the most common culprit is a dirty or faulty thermocouple (a small metal rod near the flame). Other frequent causes include poor airflow, a tripped thermal switch, or a clogged pilot tube.
Replacing a water heater igniter typically costs between $𝟕𝟓 and $𝟑𝟓𝟎 in total. This includes $𝟓 to $𝟏𝟐𝟓 for the replacement part itself, depending on whether it is a standard manual Piezo igniter or an automatic Hot Surface Igniter (HSI), plus $𝟕𝟎 to $𝟐𝟐𝟓 for professional labor.
Steps to fix a water heater pilot light that won't stay lit:
If your pilot light keeps going out, there's a chance that the gas supply has been compromised. A pilot light needs gas to continue burning—so if there's no gas, then there's no pilot light. Check the gas valve; there's a high chance it's dirty or malfunctioning.
Common Signs of a Bad Furnace Thermocouple
A: Traditional tank water heaters usually last 8–12 years, while tankless units often last 15–20+ years.
To clean a gas heater's thermocouple, shut off the gas valve and allow the unit to cool completely. Carefully access the pilot assembly, use a wrench or screwdriver if necessary to remove the thermocouple, and gently polish the tip with fine-grit sandpaper, an emery cloth, or steel wool.
If the sensor doesn't register a flame, it shuts off the gas supply as a safety measure. If your pilot light won't stay lit, a dirty or faulty thermocouple is often the culprit. Try gently cleaning it with fine sandpaper or a soft cloth. If that doesn't work, it may need to be replaced.
Learning how to replace a thermocouple allows you to troubleshoot a gas furnace or water heater when the pilot light won't stay lit. Cleaning and replacing the thermocouple can help keep the appliance running smoothly and extend its life.
PG&E offers free furnace safety inspections and gas pilot relight appointments.
Disconnect and Remove the Old Ignitor: Unplug the wire connector for the ignitor and carefully unscrew the bracket holding it in place. Install the New Ignitor: Screw the new ignitor into place and connect the wiring. Safety Reminder: Never touch the gray or black part of the new ignitor with your bare hands.
The pilot light requires a steady supply of oxygen to maintain a stable flame. The pilot light always remains burning. When it's time to heat, the gas control valve releases gas into the main burner. The thermocouple must sense enough heat from the flame to keep the gas valve open, ensuring safe operation.
Pilot Light Issues: The pilot light may go out due to a blocked or damaged thermocouple. Relighting is typically inexpensive unless the thermocouple requires replacement, which can range between $120 and $300.
SIGNS OF PILOT LIGHT ISSUES
A weak or flickering light indicates dirt accumulation or blockages in the pilot light assembly. This results in hindering gas flow. The consistent extinguishing of a pilot light is another sign that indicates a faulty thermocouple or problems with the gas supply.
You will want to clean the thermocouple with a piece of emery cloth or high grit (1000) sandpaper. This may resolve the issue. Another issue that could be causing this is the connection point between the thermocouple lead and the gas valve.
If the thermocouple gets covered in debris or corroded over time, it can no longer effectively sense the pilot flame, and furnace operation may be disrupted. Performing some simple annual cleaning of your furnace's thermocouple can optimize efficiency and safety.
Common gas water heater symptoms include no hot water (often caused by a broken thermocouple or tripped thermal switch), rumbling or popping sounds (sediment buildup), and rusty water or leaks (internal tank corrosion).
Tankless water heaters are the longest-lasting, averaging 20+ years, while the Rheem Marathon leads tank-style heaters with a lifetime warranty. Standard steel-tank models fail within 8–12 years, so maximizing longevity requires either choosing a premium model, a tankless unit, or maintaining standard units.
Is It Worth It to Repair a Hot Water Heater? Repairing a water heater is worth it when the unit is less than 10 years old, repair costs less than 50% of replacement cost, the problem is minor like a thermostat or heating element, and the tank shows no signs of rust or corrosion.
If your pilot light won’t stay lit, the most common culprit is a dirty or faulty thermocouple (the small metal rod next to the flame that signals the gas valve to stay open). To fix it: hold the gas knob down longer, clean or replace the thermocouple, or clear a blocked pilot tube.
Replacing a thermocouple is something you can do at home, only requiring an open-end wrench and screwdriver or nut driver. Safety First: Before starting, turn off the power and gas supply to the furnace.
Yes, unburned gas will leak if a pilot light goes out, but the danger level depends on the type of appliance and its safety features.