The usual cause is a shorted heating element, a stuck thermostat that keeps an element running, or a loose or corroded wire. A leak near the electrical parts or a mismatched breaker can also do it. Reset the breaker once at most. If it trips again, leave it off and get it diagnosed.
What makes a water heater trip the breaker?
Lennox lists six causes, and A. O. Smith's service guide backs up the main ones from the manufacturer's side.
### A shorted or grounded element
Inside a heating element is a coil, and the coil can break down and touch the metal sheath. Current then leaks to the tank. Lennox describes a damaged element as one of the most frequent reasons a water heater keeps tripping the breaker, because a shorted element draws far more power than the circuit is rated for. A. O. Smith's guide gives a test for this: with the power off, check resistance from each element screw to the tank. A reading of OL is fine. Any lower reading means the element is shorted to ground and must be replaced.
### A stuck thermostat
A. O. Smith says that if the elements test good, the thermostat contacts may have welded shut, which keeps the element on all the time. It also says the lower thermostat is the most likely to fail because it does most of the work. Lennox describes a stuck thermostat as one that lets an element run continuously and overload the circuit.
### Loose or corroded wiring
Lennox says loose connections arc and generate heat, which trips the breaker repeatedly. Rheem's installation checklist includes tight electrical connections and a properly grounded unit.
### A leak near the electrical parts
Lennox warns that even a minor leak near electrical components can cause ground faults. A. O. Smith's no-hot-water chart also says to check for a leak on the hot side of the plumbing if the elements and thermostats test good.
### A breaker that doesn't match the heater, or a failing breaker
Lennox says an undersized breaker can trip constantly even when the heater is fine. And sometimes the breaker itself is the weak link. Testing it means working in the panel, which is an electrician's job.
What should the breaker size be?
It depends on the heater's wattage, which is printed on the rating plate. Rheem's guide pairs breaker size and wire size for its electric heaters, and says the table is based on the National Electrical Code.
| Total water heater wattage (240 volts) | Recommended breaker | Copper wire size |
|---|---|---|
| 4,500 watts | 25 amps | 10 AWG |
| 5,500 watts | 30 amps | 10 AWG |
That's why swapping in a bigger breaker is never a fix. The breaker is sized to protect the wire, and Rheem pairs each breaker size with a wire size. A bigger breaker on the same wire removes the protection while leaving the fault in place. Rheem also says the branch circuit, with an overcurrent device and a disconnecting means, must be provided by a qualified electrician.
Grounding matters too. Rheem's caution is that water in the piping and heater does not provide enough conduction for a ground, and that non-metallic pipe, dielectric unions or flexible connectors can leave the heater electrically isolated. Its manual calls for a proper ground conductor back to the electrical panel. A heater that isn't properly grounded is a shock hazard, so leave that to an electrician too.
What can you check safely?
These steps stay on the safe side of the line.
- 1Reset it one time. Turn the breaker fully off, then on. If it trips again right away or within a short time, leave it off. Lennox advises seeing a licensed professional rather than resetting it over and over.
- 2Press the heater's red reset button. This is the high-limit reset behind the upper access panel. Turn the breaker off first. A. O. Smith says that if the button clicks, the water got hot enough to trip the energy cutoff. A heater that trips this repeatedly has a thermostat or element problem, and Rheem says a qualified service technician must investigate the cause of a high-temperature trip before the heater is used again.
- 3Look for water. Puddles, rust streaks or dampness around the access panels, the tank base or the pipe fittings suggest a leak that needs fixing.
- 4Look for burn marks, but don't touch. With the breaker off and the power confirmed dead, remove the panel and look for scorched wire insulation or melted plastic. Lennox lists burning smells, buzzing and a warm breaker panel as signs to get help now.
If you smell burning, hear buzzing, or the breaker or panel is warm, Lennox says to turn off the main switch and not reset the breaker.
### Can you test the element yourself?
If you're comfortable with a multimeter and can shut the power off safely, yes. Our page on how to test a water heater element covers the resistance test and the short-to-ground test, with the safe shutdown order. Confirm the power is off with a voltage tester first, because A. O. Smith notes that breakers can be mislabeled.
### What should you never do?
- Never keep resetting a breaker that keeps tripping. Lennox says to consult a licensed professional rather than repeatedly resetting it, and not to reset it at all if there's a burning smell, buzzing or a warm panel.
- Never install a larger breaker to stop the tripping. The breaker protects the wire, so a bigger one on the same wire leaves the fault and removes the protection.
- Never power the heater before the tank is full. After a drain, a flush or a part replacement, A. O. Smith says the tank must be completely full before power is connected, and Rheem's checklist says the water heater must be completely filled with water. Running it dry burns out an element.
- Never work on a live circuit. A. O. Smith warns that breakers can be mismarked, so check the wires with a voltmeter before touching them.
What does the fix involve, and who does it?
A shorted element is a replacement job. A stuck thermostat is a replacement job too. A loose connection means tightening or replacing the terminal, and a leak means finding where it's coming from. Rheem's manual says not to attempt repair of electrical wiring, heating elements or other safety devices, and to refer that work to qualified service personnel. That's the sensible line: you can gather clues, but the repair belongs to a licensed pro.
If the tank itself is leaking, it's time to think about replacement, and our page on whether to repair or replace a water heater helps with that decision. If the heater is old, our page on why you might have no hot water covers the other failures to expect. If the heater does need replacing, our page on the Phoenix permit rules for replacing a water heater covers what the city expects.
### What should you tell the technician?
A few details speed up the visit. Note whether the breaker trips instantly or after the heater has been running, whether it trips at the same time of day, whether you saw a leak, burning smell or buzzing, and the wattage and voltage on the rating plate. Say if the reset button clicked. Take a photo of the breaker label and the rating plate.
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