No Hot Water? A Step-by-Step Water Heater Repair Checklist

Work from the cheapest cause to the most expensive, and stop as soon as one explains what you are seeing. On a gas heater: is the pilot or igniter lit, is the gas valve open, has the thermostat been knocked down. On electric: has the breaker tripped, and has the high-limit reset button on the front of the unit popped.

Gas: start at the pilot

If the pilot is out, relight it following the label on the unit. If it lights and then dies within a minute or two, the thermocouple is the usual cause. It is the sensor that tells the gas valve the flame is real, and when it weakens the valve closes as a safety measure. That is a small serviceable part, not a reason to replace the heater.

Electric: the reset button first

There is a red reset button behind the upper access panel. If it has tripped, something caused it: most often a failed upper thermostat or an element that has shorted. Pressing it once is reasonable. Pressing it repeatedly is not: it is a safety cutout, and a heater that keeps tripping it is telling you about a fault that has not been fixed.

Hot water that runs out fast is a different fault

If you get hot water and it disappears in a few minutes, the tank is not failing to heat. It is failing to hold. On electric, the lower element has usually gone, so only the top of the tank heats. On gas, heavy sediment on the tank floor insulates the burner from the water above it, which also shows up as popping and rumbling when it fires.

The Orange County angle

Water here is hard, and hardness becomes sediment. A tank that has never been flushed builds a layer on the bottom that costs efficiency long before it causes a failure, and it is the single most common reason a heater underperforms years before its actual end of life.

When it is not worth chasing

If there is water on the floor around the base and the tank itself is weeping, the tank has failed and no repair holds. Everything above the tank (valves, thermostats, elements, thermocouples, gas controls) is serviceable. The tank is not. Shut the water and the gas or breaker off and call.

Check the mixing valve before blaming the heater

Some installations have a thermostatic mixing valve on the heater outlet, blending hot with cold to cap the delivery temperature. When one fails it can send lukewarm water to the whole house while the tank behind it is working perfectly. If the heater is new, or was recently serviced, and the water is warm rather than absent, that valve is worth ruling out first.