Why won't my water heater pilot light stay lit?
The pilot lights while you hold the button, then goes out as soon as you release it, or it stays lit for hours and then drops.
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Key takeaways
- This is usually not an emergency, but it does not fix itself and it gets worse if you leave it.
- Most likely cause: Weak or failed thermocouple.
- Do this first: Follow the label on the heater to relight the pilot once, exactly as printed.
- Call right away if you smell gas near the heater. Leave and call the gas utility.
- The repair starts with: Test the thermocouple output and inspect the pilot flame shape.
What it is
Pilot light that won't stay lit A pilot light that won't stay lit means the gas water heater's flame goes out shortly after lighting, usually because the thermocouple no longer senses heat well enough to keep the gas valve open.
It is not urgent on its own, but stop relighting after one attempt and leave the house immediately if you smell gas at any point.
The short answer
A pilot that lights and then dies within seconds is almost always a failing thermocouple. The thermocouple senses the flame and tells the gas valve to stay open, and when it weakens the valve shuts down as a safety measure. Other common causes are a dirty pilot orifice, a blocked flue or air intake, and a failed gas control valve. If you smell gas at any point, stop relighting and leave the house.
What it usually means
These are the causes we find most often, ranked from most likely to least.
- 1
Weak or failed thermocouple
Most likely
The most common single cause. It is an inexpensive part with a short replacement time.
- 2
Dirty pilot tube or orifice
Common
Dust and combustion residue starve the pilot flame so it cannot heat the sensor.
- 3
Blocked flue or restricted combustion air
Common
A blocked vent pushes exhaust back down and smothers the pilot. This one also carries a carbon monoxide risk.
- 4
Failed gas control valve
Less common
The valve no longer holds open even with a healthy signal from the thermocouple.
- 5
Draft in the utility space
Occasional
An open door, a nearby vent, or a poorly sealed room blows the pilot out.
What to do right now
- 1Follow the label on the heater to relight the pilot once, exactly as printed.
- 2Check for obvious drafts near the burner compartment and close them off.
- 3Look at the flue for visible blockage, soot, or disconnection.
- 4If it will not hold after one attempt, stop. Repeated relighting does not fix a failed sensor.
When it is an emergency
- You smell gas near the heater. Leave and call the gas utility.
- There is soot around the burner or a carbon monoxide alarm has sounded.
- The flue pipe is loose, rusted through, or disconnected.
What the fix involves
Most of these visits end with a thermocouple replacement and a cleaning of the pilot assembly. Where the flue is the problem, the venting gets corrected before the heater goes back in service, because a heater that cannot exhaust safely should not run.
- 1Test the thermocouple output and inspect the pilot flame shape.
- 2Clean the pilot assembly and orifice.
- 3Inspect the flue and combustion air path for blockage.
- 4Replace the thermocouple or gas control valve, then verify a stable flame.
What drives the cost
Every job is quoted before work begins. These are the factors that move the number on this kind of repair.
- Thermocouple replacement versus gas valve replacement
- Whether flue or venting corrections are needed
- Age of the heater and parts availability
- Access to the burner compartment
Related problems homeowners ask about
Why do I have no hot water?
Taps run cold at every fixture, or hot water disappears after a minute or two. The heater may be silent, or it may run without ever heating the tank.
Read this nextWhy is my water heater making a popping noise?
Popping, rumbling, or kettle-like sounds from the tank during a heating cycle, often loudest after heavy hot water use.
Read this nextWhy is my water heater leaking from the bottom?
Standing water under the tank, a damp ring on the floor, or rust streaks running down the outside of the jacket.
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Licenses, credentials, and company proof
- Colorado Master PlumberLicense MP-00189274
- Colorado State Plumbing ContractorLicense 2110
- Family Owned & OperatedServing Denver since 2006, 20 years
- Better Business BureauAccredited Business, A+ rating
- Angie's List Super Service Award2012 through 2017
- Serving Denver since 2006Residential and commercial properties across the metro
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Straight answers on what water heater pilot won't stay lit work costs, how fast we can get out, and what stands behind the repair.
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