Tony’s Take 💬
You know the sound—that steady hum that never stops. The furnace fan kicks on… and never shuts off. You go to bed, wake up, and it’s still going like the Energizer bunny with a caffeine addiction.
Hey folks, Tony here. I’ve worked on a lot of HVAC systems, and believe me, this is one of those problems that sounds small… until your power bill says otherwise. But don’t sweat it. I’m gonna walk you through what to check, how to fix it, and when to call for backup. If you’ve got an electric furnace, this one’s especially for you. Let’s crack into it.
Section 1: Understand How the Furnace Fan Is Supposed to Work
Before we get into what's wrong, let's talk about what's right. Your furnace fan (also called a blower motor) is supposed to kick on when there's a heat call and shut off once the temp is met. Some systems also let the fan run on its own for better air circulation, depending on your thermostat settings.
If it's running constantly, it could be:
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A thermostat setting
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A stuck relay or control board issue
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Faulty wiring
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A bad limit switch
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Or even something as simple as human error
You’d be surprised how often someone accidentally bumps the thermostat fan to "On" instead of "Auto." Don’t laugh—I’ve done it myself after crawling around an attic for hours.
Need a visual breakdown of how your blower works? Check out this furnace fan operation guide from Coolray. It gives you a solid base on normal operation.
Section 2: Step-by-Step Troubleshooting – The Right Way 🔧
Alright, roll up your sleeves. Here's how I approach it in the field:
Step 1: Check Thermostat Settings
Go to your thermostat. Make sure the fan is set to “Auto,” not “On.” If it's set correctly and still won’t shut off, move to the next step.
Step 2: Kill the Power, Inspect the Thermostat Wiring
Flip the breaker to your furnace. Pull the thermostat off the wall and look at the wiring. If the green wire (usually the fan wire) is touching something it shouldn’t, that could keep the fan running.
If you want a deeper dive, The Spruce has a solid guide on thermostat wire colors.
Step 3: Look at the Fan Limit Switch
This little guy tells your blower when to stop running after a heat call. If it's stuck in the manual override position, the fan will keep running. You can usually spot a manual/auto toggle on older models.
Step 4: Test the Control Board or Relay
On modern electric furnaces, the blower motor is controlled by a relay on the circuit board. If that relay gets stuck, the fan stays on no matter what. You might hear it click but the blower doesn’t shut off.
Testing the board takes a voltmeter and some know-how. If you’re not comfortable with that, it might be time to bring in an HVAC tech.
Section 3: When It’s a Bigger Electrical Issue
If everything else checks out and your fan’s still going 24/7, you might have a more complex electrical issue. Bad wiring, a short, or fried relay contacts are no joke. You’ll need to:
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Verify power at the board
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Check for backfeed voltage
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Inspect the blower motor capacitor
And if you need to brush up on those electrical skills, this step-by-step from Fenwick Home Services on furnace blower repairs is a gem.
Section 4: If It’s a New Thermostat or Furnace Installation
New installs? You’d be shocked how often fan wiring is just misconfigured. Especially if you’re doing DIY.
Here’s what to check:
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Is your thermostat compatible with your electric furnace?
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Did you wire the G terminal (fan) correctly?
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Are jumpers installed properly (especially if you’ve got a heat pump system)?
HVAC School has a handy explainer on low-voltage thermostat wiring. It breaks it down in plain English.
Section 5: Other Unlikely (But Real) Causes 🧠
Alright, here's the weird stuff I've seen:
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Board firmware updates (on smart thermostats) causing glitchy fan control
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Zoned systems where a damper failure triggers constant fan
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Rodents chewing through wires, especially in basements and attics
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Dirty air filters confusing the system logic and keeping airflow high
If you’ve ruled out the basics and it’s still not working, don’t ignore the oddball causes.
Section 6: Fix It or Replace It?
If you’ve gone this far and you’re dealing with an old electric furnace, it might be smarter to consider a replacement than chase down aging parts. Especially if:
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The control board is discontinued
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The fan motor hums or vibrates
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Your power bill's been climbing month after month
If that sounds like your situation, take a look at the electric furnace collection at The Furnace Outlet. Tons of solid, reliable models that won’t break the bank—or your back when it’s time to install.
Tony’s Final Thoughts 💭
A furnace fan that won’t shut off is like a song stuck on repeat—you didn’t hate it at first, but now you’re losing your mind. Whether it’s your thermostat settings, a stuck relay, or a deeper wiring issue, now you’ve got the tools to handle it like a champ.
And if your electric furnace is on its last leg, don’t waste time patching up something that’s already falling apart. Head over to The Furnace Outlet’s electric furnace lineup and treat yourself to something that works right the first time.
Thinking of replacing your electric furnace? Visit my guide: The Top 5 Signs It’s Time to Replace Your Electric Furnace.
Stay sharp out there—and remember, the fan’s only supposed to blow when it’s told to.
🛠️ Until next time,
– Tony the Trusted Tech
