Furnace Ignitor Glows but Never Lights

What You're Watching Happen

You took the panel off and watched. The ignitor glows orange, holds for a few seconds, then goes dark. No flame. The furnace pauses, tries again, maybe three times, then quits and locks out.

Homeowners describe it almost word for word. "Ignitor glows for 5-7 seconds and then goes out with no ignition, no flame, no heat." Often there's a second detail that matters more than people realize. "No clicks from the gas valve when the igniter glows."

Two fears usually ride along with this. One is gas collecting somewhere in the house. The other is getting handed a control board quote you have no way to check. Both are fair. The good news is that watching one more cycle, with your ears instead of your eyes, tells you most of what a technician is going to find.

The Sequence Your Furnace Runs

A furnace starts in a fixed order, and each step has to prove itself before the next one happens. Knowing the order tells you exactly where yours is stopping.

1. The thermostat calls for heat.
2. The inducer fan spins up and pulls air through the burner box and out the flue.
3. The pressure switch senses that airflow and closes.
4. The ignitor gets power and glows.
5. The gas valve opens.
6. Gas crosses the ignitor and the burners light.
7. The flame sensor confirms there's a real flame, so the board keeps the valve open.
8. The blower starts and sends heat into the house.

If your ignitor glows, steps one through four already worked. The thermostat called, the inducer ran, the pressure switch closed, and the board sent power out to the ignitor at the right moment. Your failure is at step five or step six. That's a small slice of the machine, and it cuts the list down fast.

Before you go any further, look at the small light behind the panel. Most furnaces flash a code naming the fault they saw, and reading it costs you nothing. We walk through what those flashes mean in furnace blinking light codes. Find out what the furnace is reporting before anybody starts pulling parts.

The Listening Test at the Gas Valve

This is the part almost nobody tells homeowners, and it's free.

At the end of the ignitor glow, the board is supposed to command the gas valve open. The valve makes a soft click when it does. Not a loud one. In a basement with the inducer running, you can stand three feet away and miss it entirely.

Old trick from the trade. Put the blade of a long screwdriver flat against the body of the gas valve and hold the end of the handle against the bone just in front of your ear. The steel carries the sound straight to you. Then run a heat cycle and listen right at the end of the glow.

If you hear the click and still get no flame, the board is sequencing correctly and gas is being asked for. So either the gas isn't arriving, or it's arriving and not catching. If you hear nothing at all, the board never told the valve to open, and the question becomes what the board is still waiting on.

Keep your hands out of the burner area while it's running and don't take anything apart to do this. You're looking and listening, nothing else. If you smell gas at any point, stop, leave the house, and call the gas utility from outside.

What You Can Check Yourself

Three things, and all of them are free.

The gas shutoff at the furnace. There's a quarter turn handle on the gas line near the unit. Handle in line with the pipe means open. Handle across the pipe means closed. It gets bumped by a laundry basket, a ladder, or somebody working near it. Two second check, and it has ended plenty of no heat calls.

Other gas appliances. Light a burner on the stove. Check the water heater. If nothing gas fired in the house is working, the problem is upstream of your furnace and the call goes to the gas utility, not to a heating company.

The rollout switch. Some furnaces have a small button with a manual reset near the burners. If it's tripped, the furnace won't fire no matter what else is right. You can press it once. Understand what it means, though. That switch trips because flame or heat went somewhere it wasn't supposed to go, usually rolling back out of the burner box instead of up the flue. It's a signal, not a nuisance. If it trips a second time, stop resetting it and get somebody out. Repeated resets are how a small problem turns into a dangerous one.

Why It's Usually Not the Board

The control board gets blamed for this constantly. It's an expensive part and it's hard for a homeowner to argue with.

But look at what you watched. The ignitor glowed. That means the board took the thermostat call, ran the inducer, saw the pressure switch close, and sent power out to the ignitor at exactly the right point in the sequence. That's a board working. A dead board doesn't produce a tidy, repeatable ignition attempt.

These are the more likely causes, in the order they usually turn out.

• A weak ignitor. Ignitors age out. A glowing ignitor is not automatically a good ignitor. It can light up bright orange and still fall short of the temperature gas needs to catch. This is the single most common cause of the exact thing you're describing.
• A dirty or failing flame sensor. If the burners light for half a second and drop back out, the sensor isn't proving flame and the board closes the valve to be safe. Some people see this as no flame at all because it's over so fast.
• A gas valve that isn't opening. Either the valve has failed or it isn't getting the signal. This is the one the listening test points at.
• Gas supply or pressure. A partly closed valve, a regulator issue, or low pressure at the unit.
• The board. Last on the list, not first.

What a Real Diagnosis Looks Like

You should be able to tell the difference between somebody who measured and somebody who guessed.

Checking an ignitor means reading its resistance with a meter and comparing that to the spec for the part. For the gas side, a manometer goes on the valve to read actual pressure while the furnace runs. The flame sensor gets a microamp reading, which tells you how strongly the sensor is seeing flame instead of whether it looks clean.

If somebody quotes you a control board without doing any of that, ask one question. What did you measure? A technician who tested will give you the number without flinching. There's no wrong answer to that question if the work actually happened.

This call spikes on the first hard freeze week around Anderson Township and Newtown. A system idles all summer, then gets asked to run every twenty minutes, and a weak ignitor that limped through last March finally can't do it. That's why the phones light up all at once on the same cold morning.

Our Repairs First approach means if the answer is an ignitor or a sensor cleaning, that's the quote you get. Our technicians are salaried and earn no commission, so nobody here makes more money by turning an ignitor into a board.

If your ignitor glows and your house is cold, we'll come find out which step is failing instead of guessing at parts. Diagnostic visits are $89, credited toward any repair you approve on the same visit. We work across Anderson Township, Mount Washington, Newtown, Mariemont, Madeira, Loveland, Milford, and Amelia. Call (513) 951-8539 or get in touch here, and our heating services page covers the rest of what we handle.