Furnace Pilot Light Won't Stay Lit: Causes and Safe Fixes
A pilot light that will not stay lit is one of the most frustrating furnace problems: the furnace works for a few minutes, then the flame dies and the heat stops. On older Houston furnaces with a standing pilot, the causes are usually small — a worn thermocouple, a dirty pilot orifice, or a draft. But a pilot problem can also signal a gas supply issue, so it pays to know which causes are safe to check and which mean you should stop and call a professional.
How a Pilot Light Works
A standing pilot is a small flame that burns continuously, ready to ignite the main burners whenever the thermostat calls for heat. A safety device called a thermocouple sits in the pilot flame and holds the gas valve open; if the flame goes out, the thermocouple cools and shuts the gas off. That safety shutoff is exactly what you want — it is also why a weak thermocouple kills the pilot again and again.
The Thermocouple: The Usual Suspect
The thermocouple is the most common cause of a pilot that will not stay lit. It wears out with heat and age, and when it can no longer generate enough voltage, the gas valve closes a few seconds after you release the pilot button. Replacing a thermocouple is a quick, inexpensive repair, and our trucks carry the common types. If your furnace is over ten years old and the pilot has started going out, the thermocouple is the first thing we test.
A Dirty Pilot Orifice
The pilot flame is fed through a tiny orifice that clogs easily with dust, rust, and soot — especially after a furnace has sat idle all summer in Houston. A weak, yellow, flickering pilot flame is the classic sign: it does not heat the thermocouple properly, so the valve shuts off. Cleaning the orifice and the pilot assembly restores a strong blue flame and usually solves the problem on the spot.
Drafts and Venting Problems
A pilot flame is small and easily blown out. A draft from a nearby vent, a cracked heat exchanger, or a flue problem can push the flame away from the thermocouple or extinguish it outright. If the pilot goes out only when the blower starts, or you notice the flame bending sharply to one side, the cause may be airflow inside the furnace rather than the pilot itself — and a cracked exchanger is a safety issue that needs inspection the same day.
Gas Supply and Gas Valve
If other gas appliances in the home are also affected, the problem may be the gas supply rather than the furnace. A failing gas valve can also starve the pilot of fuel. Both are jobs for a licensed technician: gas valves are not adjustable by homeowners, and guessing at gas pressure is dangerous. If you smell gas at any point, leave the home and call your gas utility from outside.
Standing Pilot vs. Electronic Ignition
Most furnaces built in the last twenty years do not have a standing pilot at all — they use a hot-surface ignitor or spark ignition that lights the burners only when heat is called for. If your furnace has no pilot to relight, a 'pilot won't stay lit' symptom is really an ignitor or flame sensor problem, and the fix is different. Either way, a technician with a meter can identify the fault in minutes rather than by trial and error.
The Bottom Line
A pilot light that will not stay lit is usually a worn thermocouple or a dirty pilot orifice — both quick, inexpensive repairs. What matters is knowing when to stop: if you smell gas, if the pilot goes out when the blower starts, or if the problem keeps coming back, the cause may be a gas supply issue or a cracked heat exchanger, and those need a professional the same day. Never bypass a safety device to keep a pilot lit. If your furnace is old enough to have a standing pilot and keeps needing attention, ask us for an honest assessment of a modern electronic-ignition replacement — call (281) 549-0799 any time.
How to Prevent Pilot Problems Next Winter
Most pilot problems are preventable with one habit: a pre-winter tune-up in October. During the tune-up the pilot assembly is cleaned, the orifice is cleared of dust and rust, the thermocouple is tested under load, and the burners are inspected for the soot that causes weak, yellow flames. A thermocouple that is weakening shows up on the meter long before it fails outright, so it can be replaced on your schedule instead of on the coldest night of the year. Between tune-ups, keep the area around the furnace clean and free of stored chemicals, and do not let dust build up on the unit over the summer — a quick vacuum around the furnace in September costs nothing and helps. If your furnace still has a standing pilot and is over fifteen years old, ask us about a modern furnace with electronic ignition: it uses no gas at all when idle, lights reliably every time, and removes the most common failure point in the whole system.
If the pilot problem keeps returning even after a thermocouple replacement and a cleaning, the furnace itself may be telling you it is near the end of its life. Repeated ignition failures, visible rust on the burners or heat exchanger, and a furnace that needs attention every winter are all signs that the money spent on repairs would be better put toward a replacement. A modern furnace with electronic ignition has no standing pilot to go out, uses no gas while idle, and comes with a manufacturer warranty plus our 1-year written repair warranty. When you call us, ask for both numbers — the cost of the repair and the cost of a replacement — so the decision is made with real figures rather than guesswork.
At a Glance
| Pilot Symptom | Likely Cause | What to Do |
|---|---|---|
| Pilot lights, then goes out in seconds | Worn thermocouple | Replace the thermocouple |
| Weak yellow flickering flame | Dirty pilot orifice | Clean the pilot assembly |
| Pilot goes out when blower starts | Draft or exchanger issue | Switch off and call the same day |
| Pilot will not light at all | No gas or failed gas valve | Check other gas appliances; call a technician |
| No pilot on the furnace | Electronic ignition system | Likely an ignitor or flame sensor fault |
Frequently Asked Questions
If there is no gas smell, yes — follow the instructions printed on the furnace. If you smell gas, leave the home and call your gas utility from outside.
It is one of the least expensive furnace repairs, typically in the minor repair range of $150–$450 including the visit. You get a written price before work starts.
A thermocouple that is weakening, a dirty pilot orifice, or a draft inside the furnace. If it happens more than once, have it checked rather than relighting it repeatedly.
The thermocouple should shut the gas off, which is the safety design. But if you smell gas, treat it as an emergency and leave the home.
A furnace with a standing pilot wastes gas all year. If it is over 15 years old and needs frequent repairs, a modern furnace with electronic ignition is worth pricing — call us for an honest assessment.
Service Area
Same-day heating and AC service across the Houston metro, 24/7. If you need help with your furnace or heat pump, a stocked truck is already nearby.
We dispatch across Houston, TX, including ZIP codes 77002, 77003, 77004, 77005, 77006, 77007, 77008, 77009, 77019, 77027, 77056, 77057, 77063, 77077, 77079, 77080, 77081, 77082, 77084, 77090, 77095, 77098, 77099. Call (281) 549-0799 and we will route the nearest available technician to your door.
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