A furnace that won't heat is one of those problems that feels like a disaster and usually isn't. The unit sits there, the thermostat calls for heat, and nothing happens — or something happens, briefly, and then stops. It's cold, it's inconvenient, and the instinct is to reach for the phone and book a call-out.
Before you do that, it's worth knowing that a modern furnace is a collection of replaceable parts, and the ones that fail most often are cheap, well understood, and fitted with hand tools. The inducer motor, the igniter, the pressure switch, the ignition control board — these are the usual suspects, and none of them requires you to be an HVAC engineer to replace.
What they do require is correct identification, because furnace parts are model-specific in a way that catches people out. A pressure switch is not just a pressure switch. An igniter is not universal. Get the part right, and the job is straightforward. Get it wrong, and you've got the right tool for the wrong furnace.
This roundup covers the parts that fail, across the brands you'll actually find in a home furnace — Fasco, Carrier, Goodman and the rest — so you can match the fault to the fix.
Best for: Certain Fasco and Lennox furnaces where the inducer has failed
The Fasco A331 is a replacement draft inducer blower motor, a 3.3-inch diameter unit running at 3,200 RPM on 460 volts. It replaces the inducer on certain Fasco and Lennox furnace models.
The draft inducer is the motor that pulls combustion gases through the heat exchanger and out of the flue, and it runs before the burner lights. That's the key to diagnosing it. If your furnace calls for heat and you hear nothing at all before the ignition sequence, or you hear a struggling, grinding motor, the inducer is the place to look.
It also matters for safety, not just heat. The pressure switch — which we'll come to — is watching the inducer to confirm it's actually moving air before it lets the gas valve open. So a failing inducer often shows up as an ignition lockout, because the safety chain won't let the furnace fire when the inducer isn't doing its job.
Note the 460-volt rating. That's a commercial or three-phase supply figure, so check it against your own furnace before ordering. Voltage mismatches are the most common reason an inducer motor arrives and doesn't suit the furnace it was bought for.
When you fit it, spin the new motor by hand before you wire it in and listen for anything rough. A good inducer turns freely and quietly. It's a two-minute check that confirms you haven't been sent a unit that took a knock in transit, and it saves you discovering a problem after everything's buttoned up. The mounting is usually three screws and a single electrical connector, so the physical swap is genuinely quick once the old one is identified.
Buy Fasco A331 Furnace Draft Inducer Blower Motor
Best for: Carrier furnaces running a two-speed inducer
The Carrier 326628-762 is a two-speed draft inducer motor running at 3,000 RPM on 115 volts, designed to replace the inducer on a range of Carrier furnace models.
The two-speed detail matters. Higher-efficiency furnaces modulate the inducer to match the heat demand — a low speed for a gentle call, a high speed when it's genuinely cold — and a two-speed inducer is part of that system. Replace a two-speed unit with a single-speed one, and the furnace loses a capability it was designed around.
The 115-volt rating here is the standard domestic figure, which makes this a more typical home furnace part than the Fasco above. If you've got a Carrier and the inducer has gone, this is very likely your part — but check the model number against the compatibility list, because Carrier used several inducer variants across their range, and neighbouring models sometimes take subtly different motors that look identical on the shelf.
The classic symptom is a furnace that used to be quiet and has become loud, or one that rattles for a few seconds on start-up before settling. Inducer bearings wear, and a worn inducer announces itself long before it finally stops.
That early warning is worth acting on rather than ignoring. A grinding inducer that still runs will eventually seize, and it tends to seize on the coldest night of the year because that's when it's working hardest. Replacing it while it's merely noisy, rather than waiting for it to fail completely, is the difference between a planned afternoon job and an emergency in freezing weather with no heat in the house.
Buy Carrier 326628-762 2-Speed Draft Inducer Blower Motor
Best for: Goodman, Amana and Janitrol furnaces locking out on ignition
The Goodman 20197310 Pressure Switch is compatible with a wide range of Goodman, Amana and Janitrol furnace models — the fact that Goodman owns all three brands is why one switch covers so much.
The pressure switch is the furnace's honesty check. It confirms the inducer is actually drawing air before the control board allows the gas valve to open. No proven airflow, no gas. It's a safety interlock, and it's doing exactly what it should when it stops a furnace from firing.
Which is why a bad pressure switch, or a blocked pressure switch hose, is one of the commonest causes of a furnace that inducer-runs, clicks, and then locks out without lighting. People assume ignition failure and replace the igniter, and the furnace still won't fire, because the board was never going to open the gas valve with the pressure switch unproven.
Before you replace the switch, check the little rubber hose that connects it — they crack, they clog, and they fall off, and any of those produces the identical symptom to a failed switch. If the hose is sound and the inducer is genuinely running, then the switch is the culprit.
It's also worth knowing that pressure switches are rated to a specific setpoint, measured in inches of water column, and that number has to match your furnace. A switch that looks identical but trips at the wrong pressure will either never close or never open, and either way the furnace won't run right. Check the setpoint stamped on the old switch against the new one — matching the brand isn't enough on its own.
Buy Goodman 20197310 Furnace Pressure Switch
Best for: Hayward H-Series, ED2 and ED1 style ignition
The Hayward HAXIGN1931 Igniter Assembly is a replacement compatible with H-Series induced draft, electronic ED2, and millivolt or electronic ED1 style units.
The igniter is the part that actually lights the burner, and it's a genuine consumable — it's designed to glow white-hot thousands of times over its life, and eventually it cracks or burns through. When it goes, you get everything up to the moment of ignition and then nothing: the inducer runs, the gas valve opens, and there's no flame to meet the gas.
A word of real caution here. Hot surface igniters are fragile, and the oils on your fingers will shorten the life of a new one dramatically. Handle it by the ceramic base, never by the element, and don't be tempted to clean the element with anything abrasive. Fit it, and don't touch the business end.
If your furnace lights on some attempts and not others, that intermittent behaviour is classic late-stage igniter failure. They rarely die all at once — they get flaky first, and the flaky stage is your warning to replace it before you're left cold.
Because igniters are consumable and inexpensive, this is a part worth keeping a spare of if your furnace is more than a few years old. When one fails it fails completely, and a house with no heat waiting three days for a part in the middle of a cold snap is a miserable situation that a ten-minute swap and a spare on the shelf would have prevented entirely.
Buy Hayward Igniter Assembly for H-Series and ED Style Units
Best for: Replacing Johnson G76x series ignition controls
The Fenwal 35-605606-227 is a drop-in replacement ignition control module for Johnson G76x series controls, matching the same footprint and mounting holes.
The ignition control module is the brain of the lighting sequence. It takes the call for heat, runs the inducer, checks the pressure switch, energises the igniter, opens the gas valve, and confirms the flame — in that order, every time, in a fraction of a second. When it fails, the sequence breaks somewhere, and the failure can masquerade as any of the individual components it controls.
The drop-in compatibility is the selling point. Because it matches the Johnson footprint and mounting holes, you're not modifying anything — the old one comes out, the new one goes in, the wiring transfers across. That's the difference between a fifteen-minute swap and an afternoon of adapting a part that nearly fits.
Photograph the wiring before you disconnect anything. Ignition modules have a lot of terminals, and while they're usually labelled, a photograph removes all doubt when you're reconnecting. This is the single best habit you can have when replacing any control component.
The reason a module is worth replacing rather than chasing individual faults is that it sits at the centre of everything. When the lighting sequence misbehaves in ways that don't point cleanly at one component — sometimes it lights, sometimes it locks out, sometimes it short-cycles — a failing module is often the hidden cause. If you've replaced the obvious suspects and the fault wanders, the brain of the operation is the thing left to suspect.
Buy Fenwal 35-605606-227 Direct Spark Ignition Control Module
Best for: Furnaces and AC systems with a dead control circuit
The Mars 50321 is a 75VA transformer that provides power for a heating, cooling or refrigeration control circuit, and it handles multiple input voltages — 120, 208, 240 and 480 volts.
The transformer is the part nobody thinks about until the whole control side goes dead. It steps the line voltage down to the 24 volts that your thermostat, your control board and your gas valve all run on. When it fails, you get nothing — no thermostat display, no response to a call for heat, no life at all in the low-voltage side.
That total-silence symptom is actually helpful, because it points you away from the individual components. If the thermostat is dark and nothing responds, don't start replacing boards and switches — check whether the transformer is putting out its 24 volts first. A cheap multimeter tells you in seconds, and it's the first check to make on any furnace that shows no signs of life at all rather than a specific fault.
The multi-voltage capability makes this a genuinely useful part to know about, because one transformer covers a wide range of installations. Just wire it to the correct input tap for your supply — that's the one detail to get right, and it's clearly marked.
A dead transformer is often a symptom rather than a cause, and that's the important thing to understand before you fit a new one. Transformers usually fail because something downstream shorted and drew too much current — a chafed wire, a failing gas valve, a shorted board. Fit a new transformer without finding that short and you'll cook the new one too. If your transformer died, spend ten minutes looking for the reason before you power the replacement up.
Buy Mars 50321 75VA HVAC Transformer
Because these parts interact, there's a logic to diagnosing a furnace that won't heat, and following it saves you replacing parts that were never broken.
Start at the beginning of the sequence. When the thermostat calls for heat, the inducer should run first. If nothing at all happens — no thermostat life, no inducer — suspect the transformer and the low-voltage supply before anything else. A dead control side stops everything downstream.
If the inducer runs but the furnace locks out before lighting, you're in pressure switch and airflow territory. Check the switch, its hose, and whether the inducer is genuinely moving air rather than just spinning.
If the inducer runs, the sequence proceeds, but there's no flame, you're looking at the igniter and the gas side. The igniter is the cheap, common culprit here and the first thing to check.
And if the sequence wanders — sometimes fine, sometimes not, no consistent pattern — the ignition control module that oversees the whole thing becomes the prime suspect. Following that order means you replace the failed part, not a series of good ones.
Furnace parts are model-specific, and the way to get it right is the same every time: read the numbers off the failed part and off the furnace itself; don't guess from the symptom.
The furnace has a data plate, usually inside the burner compartment door, with the model and serial number. The failed component has its own part number printed on it. Between those two, you can confirm compatibility rather than hoping for it.
Match the voltage. Home furnaces mostly run 115-volt components, but not always, and a 460-volt motor in an 115-volt furnace is a wasted purchase. The voltage is printed on the part every time.
And photograph the wiring before anything comes apart. It costs two minutes, and it saves the reconnection guesswork that turns a simple swap into a frustrating one.
Most of these parts are within reach of a careful homeowner with a multimeter and a set of nut drivers. Inducer motors, igniters, pressure switches, and transformers are mechanical swaps once you've identified them, and the satisfaction of fixing your own furnace is real.
There are limits, though, and they're worth respecting. Anything involving the gas valve itself, or a persistent fault you can't pin down after replacing the obvious suspects, is a sign to bring in someone qualified. A furnace is a gas appliance, and there's no shame in deciding a particular job is above your comfort line.
The dividing line I'd draw is this: replacing a clearly failed component that you've positively identified is a reasonable home job. Diagnosing an intermittent fault by trial and error, or working on the gas train, is not.
A furnace that won't heat feels like an emergency and is usually a twenty-dollar part and a screwdriver. The inducer, the igniter, the pressure switch, the control module, and the transformer are the parts that fail; they're all replaceable, and they're all identifiable if you read the numbers rather than guessing from the symptom.
Match the part to the furnace by model and by voltage. Handle the igniter by its base and never by the element. Photograph the wiring before you touch it. And know where your own line is — a clearly failed part is a fair home repair, and the gas train is not.
Get those right, and you'll have the heat back on in an afternoon, for the cost of a part rather than the cost of a call-out and a part.
I’m Bill Rowell, the founder of RVupgrades.com. In 2002, I launched the business to help fellow RV enthusiasts find unique and hard-to-find products. Over the years, it’s grown to offer more than 15,000 items, with a warehouse in Eastlake, Ohio. Having owned and repaired nearly every type of RV, I bring over two decades of hands-on experience to the table. For me, this isn’t just a business – it’s a passion and a way of life that I love sharing with the RV community.
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