Last updated: 2026-05-01

🛠️ Can you fix this?

DIY confidence 0%

Easy — Most homeowners

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Furnace Blower Running Constantly

Fan runs non-stop even when thermostat is off

55%

55% chance this is caused by:

Thermostat fan setting on 'ON' or stuck fan relay

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Fix it this weekend. Most parts ship same-day on Amazon.

A service call costs $150-300. This repair takes about 10-15 minutes and the part runs $40. Order the part tonight, fix it Saturday morning.

🔧 The Exact Part You Need

Fan Relay Board

$40

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Total parts cost: $40. Same-day shipping available on most items.

🔍

Find the Right Part for Your Furnace

Parts vary by model. Search with your model number for the best match.

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Tip: Add your model number (e.g. "GE GSS25GSH") for more precise results.

🔥 Parts for Furnaces move fast on Amazon — especially common failure parts like these.

🔨 Tools You'll Need

Multi-Bit Screwdriver

$22

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Easy · 10-15 minutes

Parts: $40 vs $$2,500-6,000 to replace

📋 Step-by-Step Instructions

Check thermostat — fan should be set to AUTO, not ON

If thermostat is on AUTO and fan still runs, the fan relay is stuck

Turn off power to furnace

Locate the control board inside the furnace

Find the fan relay — it may be visibly stuck or burned

Replace the relay board

Test by setting thermostat to heat

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Don't put this off.

A Furnace that's failing can cause water damage, electrical issues, or food spoilage — each costing 10x what the replacement part costs. The fix is straightforward. The part is cheap. The risk of waiting isn't.

Frequently Asked Questions

How much does it cost to fix a furnace that's blower running constantly?

The part costs about $40. If you do it yourself, that's your total cost. A professional service call would add $100-200 in labor, bringing the total to $190.

How long does this furnace repair take?

This repair is rated "easy" and typically takes 10-15 minutes. The most time-consuming part is usually accessing the component, not the actual swap.

What if this isn't the problem?

Our diagnosis is 55% likely based on the symptom you described. If replacing this part doesn't fix it, the next most common cause for "fan runs non-stop even when thermostat is off" would be related to the wiring harness or control board. In that case, consider calling a professional.

Should I just replace my furnace instead?

A new furnace costs $2,500-6,000. If yours is well under 15-20 years old, a $40 repair is far more cost-effective. If it's near end-of-life and has had multiple issues, replacement starts making more sense.

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