Why does my boiler pilot light keep going out?
If your boiler has a standing pilot light that keeps extinguishing, you’re left without reliable heat and hot water, and repeatedly relighting it gets frustrating fast. Note that many modern boilers use electronic ignition and have no pilot light at all; this issue applies to older standing-pilot models.
A pilot that won’t stay lit is usually a sign of a specific, fixable fault rather than a failing boiler. The most common culprit is a small safety component called the thermocouple.
HeatLand has serviced gas boilers across Metro Vancouver and the Fraser Valley since 1999. This guide explains why pilot lights go out, what you can safely check, and why the repair belongs to a licensed gas fitter.
The thermocouple: the usual culprit
The most common reason a pilot light won’t stay lit is a faulty thermocouple. This is a safety device that senses the pilot flame’s heat and keeps the gas valve open. When the thermocouple gets hot from the pilot flame, it signals the valve to allow gas flow. If it doesn’t sense enough heat, it shuts the gas off, which is what stops your pilot from staying lit.
Over time, a thermocouple can become dirty, corroded, bent out of position, or simply wear out. When that happens, it fails to register the flame properly and cuts the gas as a safety measure, extinguishing the pilot.
The fix is usually cleaning or replacing the thermocouple and ensuring it’s correctly positioned in the flame. While this sounds simple, it involves the gas valve and burner assembly, so in BC it must be done by a licensed gas fitter rather than a homeowner.
Draughts, blockages, and gas supply
Beyond the thermocouple, a few other issues cause a wandering or extinguished pilot. Draughts are a frequent cause: air movement from a nearby vent, window, or downdraught in the flue can literally blow the pilot flame out. If the flame flickers noticeably, a draught may be to blame.
A blocked or dirty pilot orifice restricts gas flow so the flame is weak and unstable, unable to stay lit or keep the thermocouple hot. Dust, debris, and corrosion build up over years and narrow the tiny opening.
Gas supply problems also matter. Low gas pressure, a partially closed valve, or air in the gas line after service can starve the pilot. If other gas appliances are also acting up, a wider supply issue is likely. Finally, a faulty gas valve can fail to hold the pilot open. Each of these requires a technician to test gas pressure and inspect the burner safely.
What you can safely check
There are a few safe checks before calling. Confirm the gas supply valve to the boiler is fully open and that other gas appliances in the home are working, which helps rule out a household gas issue. Look for obvious draught sources near the boiler, such as an open window or vent, though you should not modify the flue.
Many older boilers have relighting instructions printed inside the access panel. If you choose to relight the pilot, follow those instructions exactly, and never force anything. Crucially, if you smell gas at any point, stop, do not relight, ventilate if safe, evacuate, and call your gas emergency line.
Do not attempt to clean or replace the thermocouple, adjust the gas valve, or clear the pilot orifice yourself. These are gas-side repairs that, under BC regulations, must be performed by a TSBC-certified gas fitter. If the pilot won’t stay lit after one careful relight attempt, call HeatLand.
When to call a licensed technician
Call a licensed technician if the pilot light repeatedly goes out, won’t relight, or lights but extinguishes as soon as you release the control knob (a classic thermocouple symptom). Persistent problems mean a component needs cleaning or replacement.
Stop immediately and treat it as an emergency if you smell gas, hear hissing, or feel unwell, do not relight under any circumstances in that case. A repeatedly failing pilot combined with a gas smell should never be troubleshooted at home.
HeatLand’s licensed, insured, TSBC-certified gas fitters test gas pressure, clean or replace the thermocouple, clear the pilot assembly, and verify the gas valve and safe combustion on all major boiler brands. We serve Metro Vancouver and the Fraser Valley, offer emergency service, and can advise whether an aging standing-pilot boiler is worth repairing or replacing with a more efficient electronic-ignition model, with financing available.
Quick Checklist
- Confirm the gas supply valve to the boiler is fully open
- Check that other gas appliances are working normally
- Look for draughts from nearby windows or vents
- Follow the boiler’s printed relighting steps exactly, once
- Never relight if you smell gas; evacuate and call for help
- Call a licensed gas fitter if the pilot won’t stay lit
| Symptom | Likely cause | Fix |
|---|---|---|
| Pilot dies when knob released | Faulty thermocouple | Clean or replace thermocouple |
| Flame flickers then goes out | Draught near boiler/flue | Address draught source |
| Weak, unstable pilot flame | Blocked pilot orifice | Clean pilot assembly |
| Pilot won’t light at all | Gas supply / valve issue | Test pressure, service valve |
Frequently Asked Questions
Why does my pilot light go out as soon as I let go of the knob?
That’s a textbook sign of a failing thermocouple. While you hold the knob, gas flows to the pilot manually. When you release it, the thermocouple must sense the flame and keep the gas valve open. If it’s dirty, worn, or misaligned, it can’t, so the valve closes and the pilot dies. A gas fitter can replace it.
Can I replace the thermocouple myself?
It’s not advisable, and in BC it isn’t permitted. Thermocouple replacement involves the gas valve and burner assembly, and gas appliance work must be done by a licensed, TSBC-certified gas fitter. Attempting it yourself risks a gas leak or an improperly functioning safety device. A technician can do it quickly and safely.
Is it safe to keep relighting the pilot?
You can attempt one careful relight following the boiler’s printed instructions, but repeatedly relighting a pilot that won’t stay lit is not a fix and can be unsafe. Most importantly, never relight if you smell gas, evacuate and call your gas emergency line instead. If it keeps going out, have a licensed technician diagnose it.
Should I replace my old pilot-light boiler?
If your boiler is old and relying on a standing pilot, repeated pilot failures may be a sign of general wear. Modern boilers use electronic ignition, which is more reliable and efficient. Whether to repair or replace depends on the unit’s age and condition. HeatLand can assess it and outline your options, with financing available.
Reviewed by the HeatLand Heating & Cooling team — licensed HVAC contractor serving Metro Vancouver & the Fraser Valley since 1999. This article is for general guidance only. If you smell gas, suspect a carbon monoxide leak, or are unsure about any electrical or gas component, stop troubleshooting immediately and call a licensed technician or 911.