Pilot Light Keeps Going Out on Your Boiler? 5 Causes & Fixes
A repeatedly extinguished pilot light is the most common reason older boilers stop heating. Here's what causes it, what you can safely do, and when to call in a Red Seal gas-fitter.
What Does a Pilot Light Do?
Older atmospheric gas boilers — and many still in service across Vancouver, Burnaby, and New Westminster — use a standing pilot light: a small, continuously burning flame that ignites the main burner when the thermostat calls for heat. The pilot is kept alive by a dedicated small gas supply and is monitored by a safety device called a thermocouple (or sometimes a thermopile). If the thermocouple doesn't sense the pilot flame, it cuts the gas supply as a safety measure — preventing unburned gas from accumulating.
Modern condensing boilers (2005 and newer) use electronic ignition instead of a standing pilot — they generate a spark or hot surface ignition on demand. If you have a modern boiler and it won't ignite, see our boiler no heat guide or error codes page instead.
5 Causes of a Repeatedly Extinguished Pilot Light
1. Failed or Failing Thermocouple
The thermocouple is a thin metallic probe positioned directly in the pilot flame. It generates a small electrical voltage when heated — typically 15–35 millivolts — which holds the gas valve open. When the thermocouple ages, its voltage output drops. If it falls below the gas valve's minimum threshold (usually around 10–15 mV), the valve closes and the pilot goes out. A thermocouple that fails slowly may produce a pilot that holds for a few minutes then extinguishes. This is the #1 cause of pilot outage on older boilers in BC and costs around $80–$150 to replace, including labour.
2. Faulty Combination Gas Valve
The gas valve receives the thermocouple's safety signal and allows gas to flow to both the pilot and, when the main burner is called, the main gas train. If the valve's internal thermocouple seat or electromagnet is worn, the pilot won't stay lit even with a functioning thermocouple. Gas valve replacement is a licensed gas-fitter job in BC — homeowners may not modify, bypass, or replace gas valves.
3. Draught or Combustion Air Issues
Atmospheric boilers rely on a natural draught up the flue to draw combustion air across the burner. Strong winds, a downdraught from a chimney, or a partially blocked flue can extinguish the pilot. This type of intermittent outage often correlates with weather events — storms, strong east winds common in Coquitlam and Port Moody, or cold snaps. A draught diverter in poor condition can also allow downdraught to reach the pilot area.
4. Blocked or Dirty Pilot Orifice
The pilot orifice is a tiny brass fitting that meters gas flow to the pilot flame. Dust, debris, or partial blockage from a spider web (more common than you'd expect in warm-season outages) can reduce the gas flow to the point where the flame is too weak to heat the thermocouple adequately. A blocked orifice produces a very small, blue-tipped yellow flame rather than the healthy 1.5–2 cm blue flame it should produce. Cleaning the orifice requires disassembly and is done as part of a professional annual service.
5. Age and End-of-Life Conditions
Gas boilers with standing pilots that are 20+ years old often have multiple age-related issues converging — a weak thermocouple, a gas valve with worn seals, and a flue with partial blockage from years of combustion deposits. When a boiler requires multiple concurrent repairs to maintain the pilot, it's often more economical to replace the unit. Newer condensing boilers eliminate the pilot entirely, reduce gas consumption by 15–30%, and may qualify for FortisBC rebates.
What You Can Safely Do
- Relight the pilot following the manufacturer's instructions on the boiler label. This is a permitted homeowner task. Wait 5 minutes after any gas smell before attempting to relight — if the smell persists, do not relight.
- Observe the pilot flame. A healthy pilot is a steady, mostly blue flame approximately 1.5–2 cm tall. A weak, yellow, flickering, or very small flame indicates an issue worth reporting to your technician.
- Track the pattern. Note whether the pilot goes out immediately, after a few minutes, or only in certain weather conditions. This information speeds up the technician's diagnosis considerably.
When to Call a Licensed Gas-Fitter Immediately
- You smell gas near the boiler — leave the building, don't operate switches, call FortisBC at 1-800-663-9911 and 911
- The CO detector is alarming — evacuate and call 911. A failed pilot on an improperly vented boiler can cause CO to accumulate.
- The pilot won't stay lit for more than 30 seconds after multiple relighting attempts — the safety system is working but the underlying cause needs professional repair
- The boiler is 20+ years old and has had recurring pilot issues — a replacement assessment is warranted
Our Red Seal–certified gas-fitters carry thermocouples for all common residential boiler models. A thermocouple replacement can typically be completed in under an hour. If the diagnosis points to a gas valve or more complex issue, we'll provide a full written quote before proceeding.
Pilot keeps going out? We fix it today.
Call 604-359-1081 — Red Seal gas-fitters with same-day availability across Metro Vancouver.