Water Heater Breaker Keeps Tripping

Likely causes

1. 1

   Cause 1: A shorted or grounded heating element

   It's a frequent culprit. Elements sit in the water, and over the years the sheath cracks or corrodes. Once water reaches the coil inside, the element shorts to the tank and the breaker trips the moment the thermostat calls for heat. A.O. Smith lists grounded heating elements among the electrical problems to check when the breaker trips.

   A tell: the breaker holds for a while, then trips when the heater starts a heating cycle. That's the element switching on.

2. 2

   Cause 2: Loose, burned or corroded wiring

   Loose connections heat up, and heat makes them looser. You'll see browned insulation, melted wire nuts or a scorched terminal block. Lennox notes that corroded wiring is a job for a licensed electrician. Check the junction box on top of the heater and both thermostat terminals.

3. 3

   Cause 3: A failed thermostat

   A thermostat that sticks or shorts can feed power where it shouldn't. Lennox lists a malfunctioning thermostat as a cause and says to have a pro test and replace it. A stuck thermostat more often trips the red reset button on the heater than the panel breaker. Our reset button guide covers that case.

4. 4

   Cause 4: Water in the electrical parts

   A leak from the top fittings, the relief valve or an element gasket can drip into the wiring. If there's water around the heater, fix the leak first. Lennox says to have the electrical parts inspected before power goes back on. See water heater leaking from the top.

5. 5

   Cause 5: A worn or wrong-size breaker

   Breakers wear out, especially ones that have tripped many times. A breaker that's warm to the touch, buzzes or trips with the heater disconnected is suspect. On a new install, the breaker may simply be smaller than the heater needs. Lennox advises having a licensed electrician check the breaker against the heater's requirements.

What size breaker does a water heater need?

The rating plate on the side of the tank lists voltage and wattage, and the installation manual lists the matching breaker and wire. A.O. Smith's manual for its residential electric tanks says to use 10-gauge solid copper wire and to confirm the "circuit breaker rating and type are correct for this water heater". It also points installers to the National Electrical Code (NFPA 70) where there's no local code.

Tankless and heat pump units are different. A whole-house electric tankless heater can need two or three double-pole breakers; Stiebel Eltron's largest Tempra model takes three 50-amp breakers. Heat pump water heaters vary: A.O. Smith's hybrid line includes 120-volt plug-in models alongside standard 240-volt ones. Go by the label, not by what the old heater used.

Checks you can do safely

1. Look before you touch. With the breaker off, remove the upper and lower access covers and fold back the insulation. Look for scorch marks, melted plastic and loose wires.
2. Isolate the heater. If the breaker trips with the heater's wires disconnected at the panel or junction box (an electrician's job), the fault is in the breaker or circuit, not the heater.
3. Test each element for a ground. With the power off and the wires removed from the element, set a multimeter to ohms and touch one probe to an element screw and the other to the tank or element flange. Any reading means the element is grounded and has to be replaced. Our guide to testing a water heater element shows the steps.
4. Check the element for continuity. Across the two screws, an open circuit (no reading at all) means a burned-out element. That causes cold water, not tripping, but you'll want to replace it in the same visit.

Fixes

Grounded element: replace it. You'll need to shut off the cold supply, drain the tank below the element, and fit a new element and gasket of the same voltage and wattage. Never switch power on until the tank is full, or the new element can burn out dry. The steps are on replacing a water heater element.

Burned wiring or terminal block: this is electrician work. Damaged conductors have to be cut back or replaced, and the circuit checked.

Bad thermostat: replace it with a matching part and set it to about 120°F, which is A.O. Smith's factory setting.

Worn breaker: a licensed electrician should replace it with one matched to the heater and wire.

Vacuum breaker vs circuit breaker

People sometimes search for a "vacuum breaker" on a water heater and mean the electrical one. They're unrelated. A vacuum breaker is a small plumbing valve on the cold side of some heaters that lets air in if the line loses pressure, so the tank can't siphon. If yours is spitting water, that's a plumbing issue, not an electrical one, and the water heater leaking page is the better starting point.

When to call a pro, and what it costs

Call a licensed electrician or plumber if the breaker trips again after one reset, if you see any burn marks, or if you don't own a multimeter. HomeGuide's figures:

Expect a service call fee of $50 to $200 in many areas. If the tank is old and also leaking, compare the quote with water heater installation cost before you approve a repair.