Cause 1: A Failing Thermocouple
This is by far the most common cause of a pilot that relights but won't stay lit. The thermocouple is a safety sensor positioned right at the pilot flame, designed to detect its heat and, as long as it senses the flame, keep the gas valve open to allow continued gas flow to the pilot.
Why It Fails
Thermocouples wear out gradually with age and repeated heating cycles — once a thermocouple can no longer reliably sense the pilot flame's heat, the safety system interprets this as the flame being out (even if it briefly wasn't) and shuts off gas flow as designed, extinguishing the pilot shortly after you relight it. This is a deliberate safety feature working as intended, even though it's frustrating from a troubleshooting standpoint.
Why This Is Usually a Straightforward Fix
Thermocouples are a relatively inexpensive, standardized part, and replacement is typically a same-visit repair for a plumber — this is genuinely one of the more affordable water heater repairs available, not a sign of a bigger problem with the unit overall.
Cause 2: A Draft Affecting the Pilot Flame
Water heaters located near a door, an air vent, or in a drafty basement area can have their pilot flame physically disturbed by airflow, sometimes enough to extinguish it even when the thermocouple and gas supply are both functioning correctly.
How to Recognize This as the Cause
If the pilot goes out more frequently during windy weather, or specifically when a nearby door or window is open, this pattern points toward a draft-related cause rather than a component failure. Sometimes the fix is as straightforward as addressing the draft source itself — sealing a gap, adjusting nearby ventilation, or in some cases relocating what's causing the draft — rather than replacing any water heater part at all.
Cause 3: A Dirty or Partially Clogged Pilot Orifice
The pilot orifice is a very small opening that controls gas flow specifically to the pilot flame — debris or buildup restricting this tiny opening can cause a weak, unstable flame that's more prone to going out even under normal, draft-free conditions.
Why This Needs Professional Cleaning
Given how small the orifice opening is, cleaning or clearing it properly typically requires specific tools and careful handling to avoid damaging the component — this is generally a job for a plumber rather than a DIY attempt, unlike the relatively simple relighting process itself.
A Less Common but Serious Cause: Gas Control Valve Issues
If a thermocouple has been replaced and the pilot still won't stay lit reliably, or if you've noticed other unusual behavior from the unit, the gas control valve itself — a more significant and more expensive component than a thermocouple — may be the actual issue. This is less common than a simple thermocouple failure, but worth having a plumber assess directly if straightforward fixes haven't resolved a persistent pilot light problem.
What to Do While You Wait for Service
Repeated manual relighting attempts without addressing the underlying cause aren't dangerous in themselves if done correctly following the instructions on the unit, but they're clearly not a sustainable solution and typically indicate it's time to call rather than continue the cycle. If you notice any gas smell at any point during this process — beyond the very brief, normal smell during the relighting process itself — stop and follow standard gas leak safety precautions rather than continuing to troubleshoot.
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Frequently Asked Questions
Is a pilot light issue dangerous?
Not inherently, but repeated manual relighting attempts without knowing the actual cause can indicate a gas control valve issue worth having properly inspected rather than continuing indefinitely.
How much does thermocouple replacement typically cost?
It's one of the more affordable water heater repairs available, usually completed in under an hour during a single visit.
Can I replace a thermocouple myself?
It's a moderately accessible DIY repair for a comfortable homeowner, though working around gas components means many people reasonably prefer to have it handled professionally.
Why does my pilot only go out during windy weather?
This pattern points toward a draft affecting the flame rather than a failing thermocouple — addressing the draft source itself is often the actual fix needed.
Is it normal for a pilot light to need occasional relighting even on a well-maintained unit?
Very occasional relighting, especially after something specific like a power outage affecting an electronic ignition system, can be normal — frequent, repeated relighting is not and points to one of the causes covered here.
Should I try cleaning the pilot orifice myself?
This is generally better left to a professional given the very small, precise opening involved and the risk of causing damage with an improper cleaning attempt.