Your gas water heater’s pilot light may stay lit while the burner refuses to ignite. This issue can leave you with cold water and a stubborn problem to resolve. This guide explains common causes, safe diagnostic steps, and practical fixes to help you restore hot water quickly and safely. The focus is on the typical residential gas water heater with a standing pilot and thermocouple, though many steps apply to modern units with electronic ignition as well.

Overview Of The Problem

A pilot light that is continuously on but the main burner fails to ignite can result from a fault in the gas control system or a mechanical failure inside the burner assembly. In most cases, the solution involves checking the gas supply, resetting the system, or replacing worn components such as the thermocouple or gas valve. Recognize safety cues: if you smell gas, stop and evacuate, then call the gas utility or emergency services. Do not attempt repairs if gas odor is present.

Common Causes And What To Check

Understanding the typical culprits helps prioritize the troubleshooting steps. The following are the most frequent reasons a water heater won’t ignite while the pilot remains lit.

Faulty Thermocouple or Its Connection: The thermocouple senses a flame and signals the gas valve to open. If it’s loose, dirty, or failing, the valve may not allow the burner to ignite even though the pilot is lit.
Dirty Or Clogged Pilot Orifice: Debris can restrict gas flow to the main burner, preventing ignition even with a lit pilot.
Gas Control Valve Malfunction: A worn or stuck gas valve can fail to relay the signal from the thermostat to the burner.
Thermostat Or High-Limit Switch Issue: A faulty thermostat or high-limit switch can prevent burner operation after the pilot has lit.
Weak Pilot Flame: If the pilot flame is too small, it may not reliably heat the thermocouple, leading to ignition failure.
Ignition System Or Electronic Control Failure (on newer models): Some units use electronic ignition rather than a standing pilot; a fault in the igniter or control board can prevent burner ignition.
Gas Supply Problems: A restricted or shut-off gas supply will prevent the burner from lighting, even if the pilot is functioning.

Diagnostics And Safe Inspection Steps

Follow these steps to diagnose the issue while prioritizing safety and minimizing risk. If you’re unsure at any point, contact a licensed technician.

Confirm Gas Supply: Ensure the main gas valve is fully open and your home gas supply is active. If you have other gas appliances, verify they are functioning.
Relight The Pilot (If Accessible): If the unit has a standing pilot, carefully follow the manufacturer’s relighting procedure. If the pilot flame is weak or goes out, the cause is likely the thermocouple, gas valve, or dirty pilot line.
Inspect The Thermocouple Connection: Look for a loose or bent thermocouple near the pilot flame. Tighten gently if loose, but never overtighten.
Check For Dirty Orifice: A blocked pilot or burner orifice can impede ignition. With power off and gas off, visually inspect for obstruction at the pilot flame tip and burner.
Test The Thermocouple With A Multimeter: If you have measurement capability, test resistance per the manufacturer’s specs. A reading outside tolerance indicates a replacement is needed.
Inspect The Gas Valve: If you notice corrosion, seepage, or stiffness in the valve handle, it may be failing and require replacement.
Look For Error Codes (If Applicable): Some newer models show service codes on a digital display. Consult the manual for code interpretations and recommended fixes.

Do-It-Yourself Fixes You Can Try

These fixes address the most common root causes. Always shut off the gas supply and power before performing any adjustment. If you smell gas, stop and evacuate immediately.

Clean The Pilot Orifice: Use compressed air or a small brush to clear debris from the pilot orifice and flame tube. Do not use sharp tools that could damage components.
Realign Or Replace The Thermocouple: If misaligned, reposition so the tip is directly in the pilot flame. If tarnished or damaged, replace with an identical part.
Replace The Gas Valve (If Necessary): A failing valve may require professional replacement. Do not attempt a DIY valve rebuild.
Reset The System: Some units have a reset button or a reset procedure in the user manual. A reset can clear minor electronic faults.
Address High-Limit Or Thermostat Issues: If the high-limit switch or thermostat is suspected, test or replace according to the manufacturer’s guidelines.

When To Call A Professional

Certain issues require licensed expertise, especially when natural gas appliances are involved. Consider professional help if:

You smell gas or suspect a leak: Leave the area and call authorities or your gas company’s emergency line.
The pilot relight attempts fail repeatedly: Replacing the thermocouple or gas valve often needs specialized tools and knowledge.
You hear hissing, popping, or see signs of corrosion: These are indicators of ongoing gas or combustion problems.
You notice water leakage or rust around the valve assembly: Could signal a broader unit issue requiring replacement.

Preventive Maintenance And Tips

Regular upkeep can extend the life of a water heater and reduce ignition problems. Implement these practices to minimize future issues.

Annual Inspection: Have a professional inspect the burner, thermocouple, and gas valve annually.
Keep The Area Clear: Ensure adequate clearance around the unit for proper air flow and safe maintenance.
Flush The Tank: Draining and flushing the tank yearly removes sediment that can affect burner performance and efficiency.
Install A Carbon Monoxide Alarm: Protect occupants by detecting CO from gas appliances, including water heaters.
Use A Quality Thermocouple: A robust thermocouple improves ignition reliability and safety.

Key Takeaways

A water heater with a lit pilot but no burner typically points to issues with the thermocouple, pilot assembly, gas valve, or ignition controls. Start with safe, basic checks: confirm gas supply, inspect the pilot and thermocouple alignment, clean obstructed passages, and consider a component replacement if worn or faulty. If uncertainty remains or if gas-related concerns arise, contact a licensed technician promptly to diagnose and repair the system safely.