Water Heater Not Heating? What to Check on Electric and Gas Tanks

A tank water heater is a simple machine: a thermostat senses that the water has cooled and switches on either electric heating elements or a gas burner. When there is no hot water, something has interrupted that chain. Most of the time it is the power or the gas, not the tank.

Start by working out which kind you have. A gas water heater has a gas pipe running to a control valve near the bottom and a vent pipe on top. An electric one has neither, only a cable into the top or side and two screwed-on panels on the side of the tank.

First, rule out a tank that is just empty of hot water

If several showers, a load of laundry and the dishwasher ran close together, the tank may simply be used up. A. O. Smith gives these recovery times:

Wait that long with no hot water running, then test a tap. If the water is hot again, nothing is broken. The heater is small for how you used it that day.

Electric water heater: check in this order

1. The circuit breaker.Safe check

   A. O. Smith calls a tripped breaker a very common reason for an electric water heater not working. Find the water heater breaker in the panel. If it has tripped, switch it fully off and then on. If it trips again, leave it off and call an electrician. See why a breaker keeps tripping.

2. The red reset button.Take care

   Turn the power off at the breaker first. Remove the upper access panel on the side of the tank and find the red reset button at the upper thermostat. Press it firmly. If it clicks, the heater had overheated and tripped this safety switch. Put the panel back, restore power and test for hot water after the recovery time.

3. If the button trips again, stop.Technician

   A reset that keeps tripping means the water is overheating, usually because of a grounded heating element or a faulty thermostat. Those parts need testing with a meter and replacing.

4. Power is fine, reset did not trip, still no heat.Technician

   The likely causes are a failed heating element or thermostat. Testing them means working on a high-voltage circuit.

Gas water heater: check in this order

1. The gas supply valve.Safe check

   Make sure the shutoff valve on the gas pipe to the heater is open. Whirlpool notes that something as simple as the gas being turned off can keep a water heater from working. If your stove and furnace are also out, call the gas utility.

2. The pilot.Safe check

   Look through the small viewing window near the bottom of the tank. The pilot on a newer heater is much smaller than on older models and can be hard to see, so dim the room lights. If your control valve has a status light, check whether it is blinking.

3. Relight the pilot, following the label.Take care

   The lighting instructions are printed on the water heater. Follow them exactly, including any waiting time. Gas water heaters made after 2003 have a sealed combustion chamber and light with a built-in igniter button, so no match is involved.

4. The pilot will not stay lit.Technician

   The part that usually fails is the thermocouple, a sensor that detects the pilot flame and stops the gas if the flame goes out. A blocked combustion air screen can also starve the burner of air. Both are service jobs.

Match the symptom to the cause

Lukewarm water and the thermostat setting

A gas water heater has its temperature dial on the gas valve near the bottom of the tank. An electric one may have two thermostats, one for each heating element, behind the side panels, and the power must be off before you open them.

The Department of Energy notes that most households only need the water heater set at 120°F, that some manufacturers set thermostats at 140°F, and that water at 140°F is a scalding hazard. It also notes that thermostat dials are often inaccurate. To see what you actually have, run the hot tap farthest from the heater and measure the water with a thermometer.

Slow recovery and sediment

Mineral sediment settles on the bottom of the tank and slows heating. A. O. Smith recommends draining a few gallons from the tank once a year to remove it, more often with hard water. If the tank also rumbles or pops as it heats, see why a water heater makes a popping noise.

Do not touch these

• The temperature and pressure relief valve. It is the safety device that opens if the tank overheats or over-pressurizes. Never cap or plug its discharge pipe. If hot water is pouring from that pipe, turn the power or gas off and call a plumber.
• Wiring, elements and thermostats behind the panels of an electric heater, beyond pressing the reset button with the power off.
• The gas control valve and burner. Relighting the pilot by the label is the limit of safe DIY on the gas side.

When to call, and when to replace

Call a plumber or a water heater technician when the breaker or reset trips a second time, when the pilot will not stay lit, or when there is water under the tank. A leak from the tank itself usually means replacing the whole water heater.

If the heater is old and the repair is a major part, compare the quote with a new unit using the repair or replace calculator, and see how long water heaters last to find the age of yours from its rating plate.

No tank on yours? A tankless heater fails in different ways: see a tankless water heater that is not getting hot.