Faulty Thermostat: Signs, Fixes, and When to Call a Pro

When your oven won’t heat right or your water suddenly turns cold, the problem isn’t always the heating element—it’s often the faulty thermostat, a small device that controls temperature by turning heat on and off. Also known as a temperature sensor, it’s the quiet brain behind your oven, water heater, and even some dryers. If it’s off by even a few degrees, your food burns, your shower goes icy, or your energy bill spikes for no reason.

A oven thermostat, a component that regulates baking temperature by cutting power to the heating element doesn’t usually fail all at once. It drifts. You notice your cookies come out undercooked, or the oven light says 350°F but it’s really 290°F. Same with a water heater thermostat, the part that tells your tank when to fire up the heating elements. If it’s stuck, you get lukewarm showers—or no hot water at all. These aren’t guesses. We’ve seen it in dozens of repair jobs: a $30 thermostat issue mistaken for a $500 element failure.

Testing a thermostat isn’t rocket science. For ovens, you can check if the heating element glows when it should. For water heaters, you can test continuity with a multimeter—no special tools needed. But if you’re not comfortable poking around inside your appliances, don’t risk it. A bad thermostat can also mean a failing control board, a broken sensor, or even wiring damage. And if your thermostat is more than 10 years old, replacement is usually cheaper than repair.

What you’ll find below are real fixes from real jobs. We’ve got guides on how to tell if your oven’s thermostat is broken, why your water heater stops heating suddenly, and when it’s smarter to replace the whole unit instead of chasing a faulty part. These aren’t theory pages—they’re the exact steps we take when someone calls us because their oven won’t bake or their shower went cold in the middle of washing up. No fluff. No jargon. Just what works.