Why is my GFCI getting hot even though the tester shows it's wired right?

Since that green light is off but you're still getting power, the internal self-test mechanism has likely failed. GFCIs aren't just passive outlets; they have a small circuit board, a transformer, and a solenoid inside. When they get old, those components can start to draw more current than they're supposed to, or the solenoid can partially engage, creating constant heat even when nothing is plugged in. The fact that it's warm under no load is the biggest red flag. A tiny bit of warmth can be normal for older electronic devices, but if it feels "hot," that’s ussually a failing internal **transformer** or a resistor that's cooking itself. If the light is dead, the unit is basially telling you its internal protection is compromised. Even if your tester shows two lights, the GFCI might not acutally trip during a real ground fault anymore. Another possibility is that the wire connections on the side of the unit are loose. If you have a high-draw appliance like a space heater or a toaster plugged into one of those downstream outlets, all that current has to pass through the master GFCI. If the wires are "back-stabbed"—pushed into those little holes in the back instead of wrapped around the screws—the contact point is tiny. Over time, that connection oxidizes, creates resistance, and generates a lot of heat.

definatly don't wait on replacing it. When you pull the old one out, look for any discolored plastic or charred insulation on the wires. If the wires look crispy, you'll need to trim them back to fresh copper before installing the new one. Stick with a "spec grade" unit rather than the cheapest one on the shelf; they tend to handle heat dissipation much better.

I didn't realize these things had so much going on inside. I always thougt they were just simple mechanical switches. Is there a way to check if the downstream outlets are actually protected if that light is out? Like, if I hit the test button on the master and it doesn't click, does that mean the whole circuit is just a fire hazard now?

I'm definitely checking for those back-stabbed wires when I pull it out beacuse the house is pretty old. I've heard people mention using 'pigtails' instead of running the whole load through the device itself—would that help keep the heat down on the new one?

To check those downstream outlets, get a plug-in tester with its own GFCI trip button on top. If you hit that button and the power stays on, you’ve 100% lost your ground fault protection. Older units like yours were notorious for failing "closed," meaning they’d keep passing power even after the safety guts died. Modern ones are designed to "fail-safe" and lock out power completley when they're toast.

That heat is likely the internal sensing coil trying to fire but failing. When you pull it, don't be surprised if the plastic around the line or load terminals looks slightly melted. It's a textbook "end of life" failure for those older models.