Water Heater Pilot Light Won't Stay Lit: Common Causes

Before diagnosing anything else, keep these points in mind:

• Follow the shutdown or relighting procedure specified by your unit's manufacturer — never a generic or improvised one.
• If you smell gas at any point, leave the house immediately and call your gas utility from outside.
• Never attempt to diagnose or manipulate a suspected gas leak, the gas valve, or the pilot assembly beyond what your manufacturer's printed instructions cover.

A water heater pilot light won't stay lit for a fairly short list of common reasons, and identifying which one you're dealing with usually doesn't require touching anything beyond what your manufacturer's instructions already cover. This guide explains what's likely happening — relighting steps themselves are specific to your unit and are covered separately below. If you're not yet sure the pilot is actually the issue, our general guide to a water heater not hot enough covers the fuller list of possible causes.

Why This Happens

1. A Worn or Misaligned Thermocouple (Most Common)

The thermocouple is a small safety sensor that confirms the pilot flame is actually present. If it doesn't sense the flame — because it's worn out, coated in residue, or positioned slightly out of place — it signals the gas valve to shut off gas to the pilot, even though the flame may have been burning normally moments before. This is often the cause behind a pilot that lights but won't stay lit.

What helps: A technician can test the thermocouple's output and replace it if it's reading outside normal range. This is generally a minor repair, though cost varies by location and unit type — get a written quote before authorizing any work.

2. A Dirty Pilot Orifice or Tube

Dust, soot, or mineral debris can partially block the small opening the pilot gas flows through, producing a weak or unstable flame that struggles to keep the thermocouple heated enough to hold the gas valve open.

What helps: A technician can clean or clear the orifice as part of a standard inspection.

3. Drafts

Pilot assemblies are somewhat shielded, but a strong draft — from a nearby vent, a door, or the water heater's own combustion air intake — can occasionally disturb the flame enough to trigger a shutoff.

What helps: A technician can assess whether the installation location or venting is contributing, particularly if the pilot only goes out during certain weather conditions.

4. Gas Control Valve or Gas Supply Issues

Less commonly, the gas control valve itself can be at fault, or gas pressure reaching the unit may be lower than it should be. Both of these point toward causes beyond the pilot assembly itself.

What helps: This calls for professional diagnosis — testing gas pressure and valve function isn't something to attempt without the right equipment and training.

Relighting: Follow Your Manufacturer's Instructions

Every gas water heater has a specific pilot-lighting procedure, usually printed on a label attached to the unit itself. Because the exact steps and safety sequence vary by manufacturer and model, this guide intentionally doesn't provide generic relighting instructions — follow the label on your unit, or have a licensed technician handle it if you don't have access to those instructions or aren't comfortable following them.

What a Technician Checks During a Visit

Rather than guessing which of the four causes above applies, a technician typically works through them in a fairly quick sequence: testing the thermocouple's electrical output first, since it's the most common culprit; inspecting the pilot orifice and tube for debris; assessing the installation location for drafts if the other two check out; and finally testing gas pressure and valve function if everything upstream looks fine. That order roughly mirrors how often each cause turns out to be the actual problem, which is why it's worth having a technician do this rather than replacing parts one at a time on a guess.

When To Call a Professional Immediately

• You smell gas at any point.
• The pilot won't stay lit after correctly following your manufacturer's relighting instructions.
• You don't have access to your unit's specific lighting instructions.
• The pilot goes out repeatedly over a short period.

Bottom Line

A water heater pilot light won't stay lit for reasons that are often associated with a worn thermocouple, though a dirty orifice, drafts, or a gas supply issue can also be responsible. Relighting should always follow your unit's specific manufacturer instructions, and a pilot that won't hold after that is a clear sign to call a licensed technician rather than keep trying.