Water Heater Not Heating? Safe Checks for Gas and Electric

Find the label on the front of the tank. It has the lighting instructions for your model, and they are the ones to follow. Then check, in this order:

• Gas to the house: do the range burners or other gas appliances light?
• The gas valve on the pipe into the heater: the handle should be in line with the pipe.
• The control knob: not on Off, Pilot or Vacation, and set to the temperature you expect.
• The pilot: many tanks have a small window to see it. If it is out, relight it by the label, and only by the label.
• The status light on newer electronic gas controls: a flashing pattern is a code, and the label or manual says what it means.
• Power-vent models: they have a fan and need electricity, so check the outlet and the breaker.

A pilot that lights and then goes out when you release the knob usually means the thermocouple or flame sensor is not proving the flame, from wear or a dirty pilot. A pilot that keeps going out on its own can be drafts, a venting problem, or the flammable vapor sensor that newer tanks have at the combustion chamber. That sensor shuts the heater down if it detects vapors, and on some models it locks out until a technician resets or replaces parts.

Do not keep relighting a pilot that will not stay lit. Repeated relights, or any smell of gas or of something burning, are reasons to call. Working on the gas control, the burner or the thermocouple is a job for a technician.

Electric water heaters run on 240 volts and have no pilot. Start at the electrical panel: if the water heater breaker is tripped, reset it once. If it trips again, leave it off and call.

Most electric tanks also have a high-limit safety, a red reset button behind the upper access panel. With the breaker off, some homeowners press it themselves. But it trips because something overheated, usually a failed thermostat or a shorted element, so a reset that trips again means a repair.

Electric tanks have two elements. If the top one fails you get no hot water. If the bottom one fails you get a little hot water that runs out fast. Testing and replacing elements means working near live wiring and draining the tank, which is a job for a technician.

Hot water that runs out fast or never gets truly hot has its own short list. Sediment on the bottom of a gas tank insulates the water from the burner and makes a rumbling or popping sound. A broken dip tube lets cold water mix in at the top instead of the bottom. A thermostat turned down, or a mixing valve set low, does the same. In winter, colder incoming water also means a tank that seemed big enough in summer can come up short.

A smell of rotten eggs in the hot water only, not in the air, is usually a reaction between the anode rod and bacteria in the tank, not a gas leak. If you smell gas in the air, that is different. Leave the house and call 911 or the gas utility from outside.

A tankless unit that will not fire usually shows an error code on its display, and the manual lists what each one means. Common causes are a flow rate too low to trigger the burner, a gas supply problem, a blocked air intake or vent, or scale in the heat exchanger. Check that the unit has power and that the gas valve is open. Cleaning a clogged inlet filter is often listed as an owner task in the manual. Beyond that, call for service.