A water heater rarely fails without warning. Before a tank leaks or stops heating, it usually gives smaller signs that build over weeks or months. Those signs matter for a service contract because a clear written record of what you saw is easier to act on than a general sense that the unit is not right.
Listen for the rumble
Sediment settles at the bottom of a tank and hardens. When the burner or element heats the water, trapped water under that layer boils and makes popping, rumbling, or crackling sounds. A new noise, or a louder one than before, is a warning to write down. Note when it happens, whether it occurs while the heater is running, and whether hot water is slow to return after a shower.
Watch the water itself
Rust-colored water from hot taps, a metallic taste, or cloudy water that clears after standing can point to tank corrosion or a worn anode rod. A little discoloration in the first draw after a long idle period is common and does not by itself show a failing tank. A pattern that repeats is different. Record what you see and which taps it comes from.
Check the drain and the floor
Look at the drain valve, the pan under the tank if one is installed, and the floor around the base. Moisture at a fitting, a damp spot that keeps returning, or staining at a seam deserves a note. If water is actively leaking, shut off the supply as your household plan directs and have a licensed plumber assess the unit. Learn where the shut-off valves are before you need them.
Keep a short log
Use a single sheet of paper or a note on your phone. For each entry, record when it happened, what you heard or saw, what you did, and whether the problem went away. A log turns a vague complaint into specific facts. It also shows whether a fault comes and goes, which is exactly what a service provider will want to know.