Tankless Water Heater: How It Works, Common Problems, and When to Repair
When you turn on the hot tap and nothing comes out, it’s often not the faucet—it’s your tankless water heater, a compact device that heats water on demand without storing it in a tank. Also known as instantaneous water heater, it’s popular in homes where space is tight and energy bills matter. Unlike old-style tanks that keep 40–80 gallons hot all day, this system only fires up when you need hot water, cutting waste and lowering costs.
But here’s the catch: if your tankless water heater stops working, it’s rarely a simple fix. It’s not like a fridge that just needs a new seal. These units rely on precise sensors, gas valves, or electric elements, and even a tiny bit of mineral buildup can shut them down. You might see an error code flashing, hear clicking noises, or just get cold water when you expect steam. Most people assume it’s broken beyond repair—but more often, it’s a clogged filter, a tripped safety switch, or a dead thermostat. These are fixes you can sometimes do yourself, if you know where to look.
Many of the issues you’ll find in our collection relate directly to tankless systems. For example, if you’re wondering why your electric water heater, a type of water heating system that uses electricity instead of gas to heat water isn’t kicking on, the answer could be the same as for a tankless unit: a faulty thermostat, a blown fuse, or sediment blocking the flow. Or maybe you’ve noticed no hot water at all—something we cover in detail in posts about water heater not working, a common household problem that affects both tank and tankless systems. These aren’t random fixes. They’re the exact same problems you’ll face whether your heater stores water or heats it on the fly.
What makes tankless units different is how quickly they fail and how quietly. One day it’s fine. The next, you’re taking cold showers. No warning. No loud bangs. Just silence. That’s why knowing the signs matters. If your unit is over 10 years old and you’re spending more on repairs than you would on a new one, it’s time to think about replacement. But if it’s newer and the issue is just a dirty inlet screen or a reset button that needs a push—you might save yourself hundreds.
We’ve gathered real fixes from actual repairs done in Rugby and beyond. You’ll find step-by-step checks for power supply, gas line pressure, and sensor errors. We’ll show you how to read error codes on common brands like Navien, Rinnai, and Rheem. And yes—we’ll tell you when to stop trying to fix it yourself and call someone who knows what they’re doing. No fluff. No guesswork. Just what actually works.
