Is it normal for a furnace breaker to fail after only five years?

If the breaker is tripping specifically when that blower motor tries to kick over, you're almost certainly looking at an overcurrent issue at the motor itself rather than a panel problem. Since you've already swapped the breaker with a known good one and the symptoms persisted, you've effectively ruled out a weak internal spring or a faulty trip mechanism in the subpanel. A loose neutral is a common culprit for wierd ghost issues, but ussually, that shows up as flickering lights or imbalanced voltages across your legs. A clean trip during a motor start-up points directly to **high inrush current**. Your blower motor has a specific rating for Locked Rotor Amps (LRA) and Full Load Amps (FLA). If the bearings are starting to seize or if the motor windings are shorting internally, that draw is going to spike way past the 20-amp threshold the moment it tries to move.

Before you call the HVAC company, grab a multimeter with an **amp clamp** if you have one. Clip it around the hot wire for that circuit inside the panel and have someone kick the thermostat up. If you see it spike to 40 or 50 amps for a split second before it pops, the motor is definitly struggling. Also, check the start capacitor on the blower itself. A blown or leaking capacitor is a cheap part that causes the motor to sit there and hum untill the breaker gives up. It's a lot cheaper than a full motor replacement. If the motor turns freely by hand and the capacitor looks good, check the actual wiring connections at the furnace junction box. I've seen plenty of wire nuts get loose over years of vibration, causing high resistance and heat that eventually trips the thermal protection. But honestly, if the panel looks as clean as you say, the gremlin is probaly sitting right there in the furnace cabinet.

I noticed a weird humming sound for a few seconds right before the click—does that sound like a dead capacitor or is the motor just stuck? Also, could the cold weather be making the grease in the bearings thick enough to cause that extra drag? I don't have an amp clamp yet, so I’m wondering if I can just use a regular multimeter to check the draw, or is that too risky for a beginner? I'm hoping it's just a cheap part because a new furnace is definatly not in the budget right now.

Don’t try to use a standard multimeter in series for this. Most are only fused for 10 amps, and that motor startup will blow the internal fuse or fry the meter's traces before you can even get a reading. You really need an inductive amp clamp.

That humming is a sign of a stalled motor. If you can't spin the blower wheel easily by hand with the power off, your bearings are toast. Also, double-check for any debris or loose insulation stuck in the wheel. I’ve seen a simple mouse nest jam a blower tight enought to trip a breaker in seconds.