Water heater not heating: how to find the problem

A water heater that stops heating almost always has one of a handful of problems, and the fuel type tells you where to look. Gas heaters fail at the burner and its safety parts. Electric heaters fail at the power supply, the elements or the thermostats.

Start with the quick checks below. They take a few minutes and solve a surprising number of no-hot-water calls.

Quick checks for any water heater

• Look at the temperature setting. Someone may have bumped it to the lowest or vacation setting.
• Check whether the problem is the whole house or one faucet. One cold faucet points to that fixture, not the heater.
• Think about recent use. Several showers and a load of laundry can empty a tank that is working fine. Give it an hour to recover.

Gas water heater not heating

The pilot is out

On older gas heaters, look through the sight glass near the bottom of the tank. If you do not see a small blue flame, relight it by following the instructions printed on the label. If it will not stay lit after you release the control knob, the thermocouple is the likely cause.

Thermocouple or flame sensor failure

The thermocouple tells the gas valve that the pilot is lit. When it wears out, the valve shuts off the gas even though the pilot was burning. It is an inexpensive part, but gas work should be done by someone qualified.

Gas supply problems

Check that other gas appliances work and that the gas valve on the line to the heater is open. On propane, check the tank level.

Status light or error code

Newer gas heaters with electronic ignition flash a status light or show a code when they shut down. Look up the pattern in our error code guides by brand before replacing any parts.

Electric water heater not heating

Tripped breaker

Find the double breaker for the water heater in your panel. If it has tripped, reset it once. If it trips again, there is a short in an element or the wiring, and you should stop and call an electrician or plumber.

High-limit reset button

Behind the upper access panel is a red reset button on the high-limit switch. It trips when the water gets too hot. With the power off, remove the panel and insulation and press it firmly. If it keeps tripping, a thermostat or element is usually stuck on.

Failed heating element

Electric tanks have an upper and a lower element. If the upper one fails, you get no hot water at all. If the lower one fails, you get a small amount of warm water that runs out quickly. With the power off, a multimeter can check each element for continuity.

Failed thermostat

Each element has its own thermostat. A thermostat that no longer sends power to its element looks just like a bad element, which is why it is worth testing both before buying parts.

Water is warm but not hot

Lukewarm water usually points to a thermostat set too low, heavy sediment on the bottom of the tank, a broken dip tube or a mixing valve set too cool. Sediment is the most common cause on tanks older than five years, and flushing the tank often helps.

When to call a pro

Call a licensed plumber if you smell gas, if a breaker or reset button trips repeatedly, or if you are not comfortable working near gas lines or 240-volt wiring. If the heater is more than about ten years old and needs a major part, compare the repair against the cost of a replacement.