A furnace igniter that wouldn't start in Porter Ranch: the igniter was good, the control board wasn't
A furnace repair in an attic in Porter Ranch. The igniter itself was good, and after we replaced the control board, the system worked normally.
In this guide
When a furnace igniter won’t start, the igniter is the obvious suspect. In this attic furnace in Porter Ranch, though, the igniter was good. The control board that powers it was the problem, and after a new board went in, the system worked normally.
The problem: an igniter that wouldn’t start
This furnace wasn’t starting its igniter. Without a hot igniter, the burners have nothing to light them, so a furnace in that state can’t make heat.
The igniter itself was good. That’s what sent the diagnosis to the control board.
What the photo shows
This was another control board replacement, in a furnace up in the attic. In the photo, a control board is in my glove and the furnace is open behind it, wiring and all. The box from the replacement board lies on the floor, next to an anti-static bag.
How does a furnace light its burners?
Once the thermostat calls for heat, the board walks the furnace through a fixed order. First it starts the inducer fan, which pulls air through the heat exchanger and out the vent. Next it waits for the pressure switch to confirm that draft. Only then does it send power to the igniter, a small ceramic element that heats until it glows orange. With the igniter hot, the board opens the gas valve, the burners light off the igniter, and the flame sensor confirms the flame.
So the board is the switch for the igniter. If the board doesn’t send power, the igniter stays cold, however good it is.
What a cold igniter looks like from the outside
You don’t need to open anything to notice this kind of fault. On a call for heat, you’ll usually hear the inducer fan start, maybe a click from the control board, and then the burners don’t light. After a pause, the board starts over. Many furnaces give up after several failed tries, stop for a while and flash a code on the status light.
Why can a good igniter stay cold?
There are three ways it happens. One is a broken igniter: these elements are brittle, and a cracked one won’t heat. Another is a board that stops short of the ignition step because something earlier in the sequence didn’t check out, such as a pressure switch that won’t close. The third is a board that reaches the ignition step and still fails to deliver power to the igniter.
On this furnace, the igniter was good, which pointed at the board’s side. Replacing the board confirmed it.
The fix: a new control board
We replaced the control board, and after that the system worked normally.
Igniters do wear out, so a cold igniter often gets replaced first. Here, a new igniter would have stayed just as cold as the old one, because the problem was the power that feeds it. Knowing the igniter was good is what pointed the job at the board.
We wrote up a similar board failure in Burbank, where a Goodman furnace’s board couldn’t sense its flame. If a board is the suspect on your system, it’s also worth knowing that some board faults can be repaired instead of replaced.
What can you check before you call?
Start with the thermostat: HEAT mode, set a few degrees above room temperature, fresh batteries if it takes them. Then check the furnace switch, which looks like a light switch near the furnace, and the breaker in your electrical panel. A clogged filter is worth replacing too, since it can cause shutdowns of its own.
Most furnaces have a status light on the control board that you can see through a small window in the lower door. Count the blinks, and tell us the pattern when you call.
With an attic furnace, only go up if there’s a safe walkway and good light. If reaching it means stepping across ceiling joists, leave it for the technician. Either way, don’t open the burner compartment or touch the igniter: it’s brittle, and it gets hot enough to burn. If you smell gas, leave the house and call the gas company from outside.
When to call
Call if the furnace makes its usual startup sounds but the burners don’t light, or if the status light keeps blinking a code.
Furnace repair in Porter Ranch
We repair gas furnaces in Porter Ranch and across the San Fernando Valley, Hollywood and the Westside, attic installations included. The $85 service call is credited toward the repair if you go ahead, and repairs carry a 30-day labor and 90-day parts warranty. CA BEAR registered (#A 50636), EPA Section 608 Universal certified, $1M insured. See our HVAC services, read more about our work in Porter Ranch, or call (213) 205-2055.
FAQ
Why won't my furnace igniter glow?
Either the igniter is broken or it isn't getting power. The control board powers it only after the earlier safety checks in the startup sequence pass, so a cold igniter can also trace back to those checks or to the board itself. On this attic furnace in Porter Ranch, the igniter was good, and a new control board got the system working normally.
Can a bad control board stop the igniter from working?
Yes. On a furnace with a hot surface igniter, the board sends the igniter its power at a set point in the startup sequence. If the board fails to do that, a good igniter stays cold. That's what happened on this furnace in Porter Ranch: the igniter was good, and replacing the board fixed it.
How do you tell a bad igniter from a bad control board?
The igniter can be checked on its own, and the board's output can be checked at the moment it should be powering the igniter. If the igniter is good and isn't getting power at that step, the board's side is next. On this furnace, the igniter was good, and a new board solved it.
Can I replace a furnace igniter myself?
We don't recommend it. The igniter sits in the burner compartment of a gas appliance, it can crack if it's handled, and on this furnace a new igniter wouldn't have helped, because the old one was good. Check the thermostat, the filter and the furnace switch, count the status-light blinks, and call.
Do you repair attic furnaces in Porter Ranch?
Yes. We repair gas furnaces in Porter Ranch and across the San Fernando Valley, attic installations included. The $85 service call is credited toward the repair if you go ahead, and you get the price after we diagnose the furnace on site. Call (213) 205-2055.
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Call (213) 205-2055 or text a photo of the unit and its model sticker.