Gas smell or alarm?
Leave and call the utility or emergency service from outside.
Boiler pilot safety check
Boiler Pilot Light Out? Check Safety Before Relighting
If a boiler pilot light is out, treat gas smell and carbon monoxide safety first. Only relight by the boiler label instructions, and stop if the pilot will not stay lit or the burner behaves oddly.
Common branches are a draft or outage, dirty pilot, weak thermocouple, gas supply interruption, or a safety control doing its job.
The key split is one safe relight after a simple outage versus a pilot that keeps going out or will not prove flame.
Don’t start with: Do not hold controls down repeatedly, bypass a thermocouple, or open burner compartments beyond the labeled user relight access.
Gas smell or CO alarm?leave first and call for help from outside.
Pilot will not stay lit?stop relighting and preserve the timing clue for service.
Do this first
- Check for gas smell before touching the boiler.
- Confirm a working carbon monoxide alarm is nearby.
- Read the boiler label for the exact relight sequence and required wait time.
- Look through the normal sight opening only; do not remove sealed burner covers.
- Stop after one failed relight or if the pilot will not stay lit.
Last reviewed: 2026-06-28
Pilot-light sorter
Pilot out after outage?
One labeled relight may be reasonable if there are no unsafe clues.
Pilot lights then goes out?
Thermocouple, pilot flame, draft, or safety-control service branch.
Pilot flame yellow or lazy?
Combustion and cleaning branch; stop homeowner work.
Main burner lights roughly?
Shut down and call for service.
Pilot clues without opening the boiler
The sight opening, flame shape, and carbon-monoxide safety context matter more than buying a thermocouple from a guess.
Before you buy anything
Confirm whether the pilot went out once, will not stay lit, has an unstable flame, or is tied to burner behavior before matching any exact part.
Start with the safety split
A pilot outage can be routine after an interruption, but it can also be a combustion, draft, or gas-control problem. The unsafe clues decide whether troubleshooting stops immediately.
- Gas smell means leave; do not relight.
- A carbon monoxide alarm means leave and call emergency help.
- A yellow, lifting, lazy, or unstable flame is not a cleaning project from the outside.
- A pilot that will not stay lit has already given you the service clue.
Relight only by the boiler label
Older standing-pilot boilers can have different lighting steps. The label on the boiler controls the wait time, knob position, and sequence.
- Use the exact instructions on the appliance label.
- Wait the required time after any failed attempt.
- Use one careful attempt only if there is no gas smell and the area is safe.
- Do not keep holding the pilot button to force operation.
Pilot-light result map
The result after one safe attempt is the diagnosis path. Timing matters: goes out immediately, holds then fails later, or lights but flame looks wrong.
- Record whether the pilot lights at all.
- Record how long it stays lit after releasing the control.
- Photograph the visible flame only if the normal sight opening allows it safely.
| Pattern | Likely branch | Next move |
|---|---|---|
| Out after power or gas interruption | Simple restart possible | Use one labeled relight if safe. |
| Lights, dies when button released | Thermocouple or flame-proving path | Stop repeated attempts. |
| Holds briefly, later goes out | Draft, pilot, thermocouple, or safety path | Record timing and book service. |
| Yellow or unstable flame | Combustion or pilot cleaning path | Shut down and call service. |
| Burner booms or rolls out | Unsafe ignition/combustion | Shut down and call urgently. |
What not to do first
The usual expensive miss is treating every pilot outage like a thermocouple. In practice, watch for the exact field clue: whether the flame lights, how long it holds after you release the control, and whether the main burner lights smoothly.
- Do not hold the pilot control down repeatedly to force the boiler to run.
- Do not defeat, jumper, or tape any thermocouple or safety switch.
- Do not brush, bend, or move pilot parts unless a qualified boiler tech is servicing the burner.
- Do not relight again if the same pilot outage returns.
Why thermocouple guesses go wrong
A weak thermocouple is possible, but the thermocouple only proves the flame it is given. A dirty pilot, draft issue, gas-pressure issue, or misaligned flame can mimic the same symptom.
- Do not buy a thermocouple until the flame shape and contact are diagnosed.
- Do not sand, bend, or reposition pilot parts from a guess.
- Do not remove burner assemblies to reach a pilot part.
- Ask the technician to check pilot flame, thermocouple output, safety controls, and draft together.
When the pilot clue points beyond DIY
Pilot and burner problems sit at the boundary between comfort troubleshooting and combustion safety. The homeowner job is to stop safely and preserve the clue.
- Stop after one failed relight.
- Stop if the pilot goes out again the same day.
- Stop if the boiler also locks out, smells abnormal, or makes delayed-ignition noise.
- Call promptly if the boiler is the home's only heat source.
- Boiler Burner Lights Then Shuts Off — Use when the main burner starts but cannot keep running.
- Boiler Locked Out After Outage — Use when the issue began after a power interruption.
Tools You May Need
These tools help you see and document outside clues while keeping combustion and carbon-monoxide safety first.
Boiler-room flashlight
Helps when: Helps read the pressure gauge, pilot area, relief outlet, valve positions, and fault display without opening covers.
Skip it when: Skip close inspection if the boiler is leaking near electrical parts, smells like gas, or has locked out again.
Compare flashlights on Amazon
Carbon monoxide alarm
Helps when: Adds a safety check around any combustion appliance when pilot, burner, venting, or flame problems are suspected.
Skip it when: Skip troubleshooting and leave immediately if an alarm sounds, you feel symptoms, or the boiler flame behaves abnormally.
Compare carbon monoxide alarms on Amazon
Notebook or phone notes
Helps when: Records pressure readings, reset timing, fault lights, leak timing, pilot behavior, and what changed first.
Skip it when: Skip buying one if clear photos and a written symptom timeline are already ready for the technician.
Compare notebooks on AmazonAs an Amazon Associate I earn from qualifying purchases. Repair Riot may earn a commission at no extra cost to you.
FAQ
Can I relight a boiler pilot myself?
Only if the boiler has standing-pilot relight instructions, there is no gas smell or carbon monoxide alarm, and you follow the label exactly. Stop after one failed attempt.
Why does the pilot go out when I release the button?
That often points to flame proving, such as a thermocouple that is not being heated properly or a pilot flame problem. Repeated attempts are not the fix.
What color should a boiler pilot flame be?
A healthy pilot is typically small, stable, and mostly blue. Yellow, lazy, lifting, or unstable flame behavior needs service.
Is a bad thermocouple always the cause?
No. Draft, dirt, pilot alignment, gas supply, and safety controls can create the same symptom.
What should I tell the technician?
Tell them when the pilot went out, whether it relights, how long it stays lit, flame color, recent outage history, and any burner noise or odor.
Can I keep running the boiler while checking this?
Only if there is no gas smell, carbon monoxide alarm, leak near wiring, relief-valve discharge, breaker trip, overheating, or repeat lockout. Stop and call for service when any safety clue appears.
What should I photograph before calling a technician?
Photograph the pressure gauge, display or fault light, first wet point if water is involved, thermostat call, pilot or burner clue from outside the cover, and the timing of the symptom.
What makes this a service-call problem?
Recurring pressure loss, relief discharge, boiler-body leakage, repeat lockout, pilot or burner trouble, electrical symptoms, or any check that requires opening a boiler compartment belongs with a qualified boiler technician.
How this guide was built
Repair Riot reviewed this page around standing-pilot outage checks, relight boundaries, thermocouple and pilot-flame clues, combustion safety, and carbon monoxide stop points. The source links support boiler maintenance and carbon monoxide safety context; the diagnostic sequence is original guidance.
- DOE furnaces and boilers — supports boiler heat distribution, controls, maintenance, and combustion-system boundaries.
- ENERGY STAR HVAC maintenance checklist — supports safe homeowner observation and professional heating-system maintenance.
- CDC carbon monoxide basics — supports carbon monoxide safety around combustion appliances and emergency stop points.