Signs of hot water heater failure include inadequate hot water supply, fluctuating water temperatures, rust-colored water, unusual noises like popping or rumbling, visible leaks around the tank, and a sudden increase in energy bills. Corrosion, sediment buildup, or a malfunctioning heating element can cause these issues. If you notice any of these signs, it's essential to address them promptly. Regular maintenance, such as flushing the tank and inspecting components, can help prevent sudden failures and extend the lifespan of your water heater.