No Hot Water: Why Your Water Heater Stopped Heating

First, rule out the obvious

Before you take anything apart:

• Is it every tap or just one? If the kitchen runs hot and the shower doesn't, the heater is fine and the problem is the shower valve. See hot water everywhere except the shower.
• Did everyone just shower? A tank needs time to recover. A.O. Smith puts recovery at about 30 to 40 minutes for gas tanks and 60 to 90 minutes for electric. If the water's coming back slowly, wait an hour before you go hunting.
• Is the thermostat turned down? Someone bumps the dial, or a vacation setting was never undone. A.O. Smith recommends 120°F as the balance of heating speed, cost and scald safety.
• Is there water on the floor? A leak changes the job. Go to water heater leaking instead.

Electric water heater: the usual causes

Electric heaters are simpler than they look. Power comes in, passes a safety switch, and feeds two heating elements, each with its own thermostat.

1. 1

   Cause 1: Tripped breaker

   A.O. Smith calls a tripped breaker "a very common reason" an electric water heater stops working. Check the panel for a double breaker that's off or sitting in the middle. Reset it once. If it trips again, stop. Something is shorted, usually an element, and resetting it over and over won't fix it. Our page on a water heater breaker that keeps tripping covers what to check.

2. 2

   Cause 2: The red reset button (ECO)

   The high-limit switch, which A.O. Smith calls the Energy Cut Off, sits behind the upper access panel. To reset it, turn off the breaker, take off the upper access panel, and press the red button firmly until it clicks. A click means it had tripped.

   Here's the catch. That button trips because the water got too hot, often from a grounded element or a bad thermostat. If it trips again within days, the reset isn't the repair. More on that on our water heater reset button page.

3. 3

   Cause 3: A burned-out element or bad thermostat

   If the power's on and the reset holds but the water stays cold or barely warm, an element or thermostat has probably failed. Lukewarm water that runs out fast usually points to the lower element. No heat at all often means the upper element or the upper thermostat, since the upper thermostat controls power to both elements.

   You can test elements with a multimeter, power off. The steps are in how to test a water heater element.

Gas water heater: the usual causes

1. 1

   Cause 1: The pilot is out

   Look through the sight glass near the bottom of the tank. No flame means the pilot is out. Check that the gas valve to the heater is open before you try to relight it. If you have other gas appliances, see whether they're working too. If the stove won't light either, it's a supply problem, and that's a call to the gas company.

   Relighting steps are printed on the label on the tank. If the pilot lights but goes out when you let go of the knob, the thermocouple is the usual suspect. See pilot light won't stay lit.

2. 2

   Cause 2: The pilot is lit, but the burner won't come on

   This one confuses people. The pilot is a small flame. The burner is the big one that actually heats the water. If the pilot's burning and the water's cold, the gas control valve may not be opening, or the burner isn't getting enough air. A.O. Smith says blocked air screens or filters starve the burner and should be cleared. A faulty gas control valve needs a professional. We walk through it on pilot light lit but no hot water.

3. 3

   Cause 3: Dirty burner or flue

   A burner caked with rust and debris won't light reliably. A.O. Smith suggests cleaning the burner assembly at least once a year, with the gas and water off first. Heavy buildup or damage is a job for a pro.

Tankless: a different list

Tankless units usually tell you what's wrong with an error code on the display. Ignition failures come down to gas supply, venting or the ignition parts. Scale is the other big one in hard water areas, and A.O. Smith recommends descaling once a year, especially in hard water areas. If you've got a code, look it up first. Rinnai owners can start with our Rinnai error codes guide.

When to call a plumber

Call when:

• You smell gas, or the pilot won't stay lit after a new thermocouple.
• The breaker or reset button trips again after one reset.
• You'd rather not open the electrical covers on the heater. That's a perfectly good reason.
• The tank is old and rusty at the base, or already leaking.

HomeGuide's figures put a typical standard-tank repair at $150 to $700, with a national average of $455. Expect a call-out fee of $50 to $200 on top in many areas. Common parts behind a no-hot-water call:

If the quote on an old tank creeps toward the cost of a new one, compare it with water heater installation cost before you say yes.