If your water heater pilot goes out occasionally and relights normally, that’s usually a draft or minor gas pressure issue. But say the pilot lights and won’t stay lit after you release the button. Or it goes out repeatedly within hours or days. That points to a component problem that needs diagnosis.
This guide covers the specific causes of a pilot that won’t stay lit. It shows how to identify which one you’re dealing with, and what to do about each.
If you haven’t yet tried relighting the pilot, start with our pilot light relighting guide first. This guide picks up from there — you’ve attempted a relight, and the pilot goes out as soon as you release the button, or within a short time.
The Thermocouple: The Most Common Culprit
The thermocouple is a safety device — a small metal probe that sits in the pilot flame. When the flame heats it, it generates a small voltage (millivolts). That voltage signals the gas valve to stay open. When the flame goes out and the thermocouple cools, the voltage drops and the gas valve closes. Gas stops flowing, which prevents unburned gas from accumulating if the pilot goes out unnoticed.
A working thermocouple holds the gas valve open as long as the pilot is burning. A failing one doesn’t generate enough voltage to do that.
Signs the thermocouple is failing:
- The pilot lights and burns normally while you hold the button, then goes out within 30–60 seconds of releasing it
- The pilot stays lit for a day or two, then goes out on its own and needs relighting
- Relighting attempts are inconsistent — sometimes it holds, sometimes it doesn’t
What to check first: the thermocouple tip needs to sit directly in the pilot flame — not near it, in it. Maybe the thermocouple has shifted, so the tip rides the edge of the flame rather than sitting fully engulfed. Then it won’t heat adequately. With the flame lit, look at the pilot assembly using a flashlight. Confirm the tip sits in the flame. If it’s bent or shifted, gently reposition it so the tip centers in the flame.
Testing the thermocouple: A plumber can test its output with a multimeter. A functioning thermocouple generates 25–30 millivolts; a failing one reads significantly lower. If it tests weak, replacement is straightforward and inexpensive.
Replacing the thermocouple: Thermocouple replacement is a DIY-accessible repair for a reasonably handy homeowner. The thermocouple screws or clips into the gas valve and sits in the pilot bracket. Shut off the gas supply, disconnect the thermocouple from the valve (usually a threaded nut), unclip it from the pilot bracket, and install the replacement. Universal thermocouples are available at hardware stores for $10–$20; make sure the replacement is the correct length. If you’re not comfortable working around gas connections, a plumber can do this quickly and inexpensively.
The Gas Valve
If the thermocouple tests fine and is correctly positioned but the pilot still won’t stay lit, the gas valve itself may be faulty. The gas valve is the control box that regulates gas flow to both the pilot and the main burner. When it fails, it may not hold the pilot circuit open even with a functioning thermocouple signal.
Gas valve failure is less common than thermocouple failure, but it does occur, particularly in older units. The distinction matters for the repair decision. A gas valve replacement costs $150–$300 for parts alone. On a water heater that’s 10+ years old, that often approaches or exceeds the case for replacing the whole unit. If a new thermocouple doesn’t resolve a pilot that won’t stay lit, have a plumber test the gas valve first. Then decide whether to repair or replace.
Dirty or Blocked Pilot Orifice
The pilot orifice is the small opening at the end of the pilot tube where gas exits and ignites. Mineral deposits — common in Santa Cruz’s moderately hard water environment, though less directly since it’s the gas rather than water running through this component — and dust or debris can partially block the orifice and produce a weak, irregular pilot flame.
A weak pilot flame that flickers or doesn’t fully engulf the thermocouple tip can cause the same symptoms as a failing thermocouple: the pilot lights, but the thermocouple doesn’t get hot enough to maintain the valve signal.
Signs of a dirty orifice: The pilot flame is visibly small, flickering, or orange/yellow rather than a steady blue. A healthy pilot flame is predominantly blue with a small yellow tip.
Cleaning a pilot orifice involves carefully removing it and clearing the opening with compressed air or a fine needle. This is a plumber’s job — incorrect reassembly creates a gas leak risk.
Draft and Airflow Issues
A pilot might light normally and hold for days or weeks, then go out seemingly at random. That’s often a draft problem rather than a component failure.
Santa Cruz’s coastal wind is a real variable. Garages, utility rooms, and closets that aren’t tightly sealed develop airflow patterns that can extinguish a pilot. That’s especially true during windy periods. Does the pilot go out more often in winter or on windy days, then relight normally each time? Then the problem is environmental rather than mechanical.
What to check:
- Are there gaps, vents, or openings in the walls or doors near the water heater?
- Does the pilot go out more often during windy weather?
- Is the unit in a location with significant air movement (near an HVAC register, near a frequently opened door)?
A draft hood deflector or repositioning nearby vents can help. Sealing significant gaps in garage walls or utility room doors addresses the root cause.
A note on combustion air: gas water heaters require a supply of fresh air for combustion. Sealing a utility space too tightly can cause a different problem — inadequate combustion air causes the burner to run poorly and can extinguish the pilot. The goal is eliminating direct drafts, not airtight sealing.
Condensation on the Thermocouple
In humid conditions — common in coastal Santa Cruz — condensation can occasionally form on the thermocouple or inside the combustion chamber. That moisture cools the thermocouple enough to interrupt the signal. It’s more likely in a new installation that hasn’t run long enough to dry out. It can also follow an extended shutdown.
If condensation is the cause, the pilot should hold normally once the unit has been running for an hour or two. This is typically a one-time or occasional issue rather than a recurring one.
When the Pilot Won’t Light at All (vs. Won’t Stay Lit)
This guide focuses on the pilot lighting, but not staying lit. If the pilot won’t ignite — no flame at all despite gas being on and the correct procedure being followed — the issue is more likely a blocked pilot tube, a faulty piezo igniter, or a gas supply problem. See the relighting guide for those scenarios.
When to Call a Plumber
Call a plumber for pilot light issues when:
- Thermocouple replacement didn’t resolve the problem
- You smell gas near the unit at any point
- The pilot flame is yellow or orange rather than blue (indicates combustion issues)
- The unit is making unusual sounds during burner operation
- The water heater is more than 10 years old and has had repeated component failures — at that point, replacement is often the better economic decision
Eco-Flow Plumbing Inc. handles water heater repair and service throughout Santa Cruz County — Santa Cruz, Live Oak, Aptos, Capitola, Soquel, Scotts Valley, Seabright, Felton, Boulder Creek, and Watsonville.
Contact Eco-Flow Plumbing to schedule service. Or call directly: (831) 818-6331.
