How to Light the Pilot on a Furnace, Safely

By Ray Bennett · Updated 2 October 2026 · 5 min read · Checked against the maker’s manual

How to Light the Pilot on a Furnace, Safely

Short answer

First make sure your furnace even has a pilot, because most made since about 1990 light themselves and have nothing to light by hand. If yours has a knob marked OFF, PILOT and ON, turn it off, wait five minutes, then hold it on pilot while you light the flame, and keep holding for a full minute.

Lighting the pilot on a furnace takes about five minutes, and the five minute wait in the middle of it is the part nobody should skip. But before any of that, there is one thing worth checking, because it saves a lot of people from hunting for something their furnace does not have.

Most furnaces built since about 1990 light themselves. There is no pilot burning, nothing to hold a match to, and no knob to turn.

Does your furnace even have a pilot?

Only the first one has a pilot you light. The other two light themselves and there is nothing to do by hand.

Open the front panel and look at the gas valve, the block the gas pipe runs into.

A knob marked OFF, PILOT and ON means you have a standing pilot, a small flame that burns all the time. That is the furnace this page is about, and the lighting instructions are usually printed on a label inside the door as well.

No such knob means the furnace lights itself, either with a ceramic bar that glows orange or with two electrodes that click and spark. There is nothing for you to light. If it is not firing up, the fault is elsewhere, and on that kind of furnace the usual one is the flame sensor: why a furnace lights then shuts off after five seconds.

Before you start

What to carry: a torch, and a long lighter or long matches if there is no igniter button. Kneeling pad if the furnace sits low. Five minutes of work, five minutes of waiting.

Turn the thermostat right down first so the furnace cannot try to fire while your hands are inside it.

If you smell gas, stop Leave the house, leave the door open, and call the gas company from outside. Do not touch a light switch, a phone or the furnace. A pilot that will not light is a small job, gas collecting in a room is not.

Light it, in this order

Check 1

Turn the gas knob to OFF and wait five minutes

Push the knob down slightly if it will not turn. Then leave it.

Some gas, propane in particular, is heavier than air and it settles in the bottom of the furnace cabinet, which is exactly where you are about to make a flame. Five minutes clears it, and Trane says to wait at least that long. Use the time to find the pilot assembly: a small hooded burner near the main burners with one thin rod sitting in it.

Check 2

Turn the knob to PILOT and hold it down

Some furnaces have a separate red reset button instead. Either way, it has to stay pressed the whole time you are lighting.

Check 3Ten seconds

Light it while you hold

If there is an igniter button, click it once a second. If there is not, hold the long lighter to the pilot hood.

Keep your face out of the opening and light it from the side, not from above.

Check 4

Keep holding for a full minute

The rod sitting in the flame has to get properly hot before it can hold the gas valve open by itself. Thirty seconds is often not enough. Sixty is.

Let go slowly. If the flame stays, turn the knob to ON, put the panel back, and set the thermostat to heat.

It lights, then goes out the moment I let go

That usually points to the thermocouple, the rod in the flame. It makes a tiny current when it is hot, and that current is all that holds the gas valve open.

Give it longer first. Two minutes of holding, not one. A weak thermocouple sometimes just needs longer to reach temperature, which tells you it is on the way out.

Look at the flame. It should be blue, steady, and big enough to wrap the top half inch of the rod. A small yellow flame that dances about will not hold anything open, and that is a blocked pilot orifice, not a bad thermocouple.

Then change the rod. A cheap part, one nut at the gas valve and a clip at the bracket. It is the same part and the same job as on a gas water heater: the thermocouple test with a meter.

The pilot is lit but the burners never come on

That is a different fault, and the pilot has done its part.

Is the thermostat calling? Set it well above room temperature and listen for a click at the furnace.

Is the filter blocked? A furnace that overheats trips its limit switch and refuses to fire again until it cools. A grey filter is the first thing to check when a furnace stops in cold weather.

Is the flue clear? Birds, nests and snow block flues, and a vent safety switch will not let the furnace light if the exhaust cannot get out.

Why it went out in the first place

A standing pilot that has burned for years does not go out for no reason.

A draught. A door left open, a new extractor fan, a windy night in an old house.

A dirty orifice. Dust and lint choke the little gas opening, the flame shrinks, and one day it does not come back.

The thermocouple ageing. It wears out like any part. When it weakens, it drops out on the coldest night, which is the night you notice.

The gas was off. Worth asking before anything else. A supply interruption or somebody turning a valve puts out every pilot in the house.

Questions people ask

How much gas does a standing pilot use?

Not much, and some people turn it off in summer to save it. If you do, remember it has to be relit before the first cold night.

Can I light it with a normal lighter?

Only if you can reach the pilot without putting your hand inside the burner area. Long lighters are cheap and exist for exactly this.

The knob will not turn to PILOT.

Push it down while you turn. If it still will not move by hand, Williams’ lighting label says never to force it or use tools, and to call a technician.

It lights, runs, then stops after a few minutes.

Not a pilot fault. That is an overheating furnace or a flame rollout switch, and the filter is the first thing to look at.

Should I replace an old standing pilot furnace?

Only when it needs a big part. They are less efficient than a modern one, but a working furnace with a cheap fix is cheaper than any replacement.

Sources: Williams Comfort Products owner's manual for the Forsaire counterflow gas wall furnace (standing pilot lighting instructions and troubleshooting chart), and Trane "How to Check the Pilot Light on a Furnace" and "Furnace Main Burner Shuts Off After Ignition"