In short
A water heater element is the electric resistance rod that heats an electric tank; most tanks have an upper and a lower one, and only one runs at a time. A failed lower element means hot water runs out fast, a failed upper element means none at all, and a grounded element trips the breaker. Replacement runs $200–$400.
Electric tank water heaters have no burner and no vent. The heating is done by one or two metal-sheathed rods that screw or bolt through the side of the tank and sit directly in the water, each behind its own access panel and controlled by its own thermostat. They are standard in homes without a gas line, in many condos and townhouses, and on rural properties beyond the gas mains.
How the upper and lower elements share the work
Only one element is on at any moment. The upper thermostat has priority: it heats the top of the tank first so some hot water is ready quickly, then passes power down to the lower thermostat and element, which heat the rest and do most of the day-to-day work. Because they never run together, the heater draws the wattage of one element, not two.
The wattage is printed on the tank's rating plate and stamped on the element itself. At 240 volts, a good 4,500-watt element measures about 12.8 ohms and a 3,000-watt element about 19.2 ohms. Either should show no continuity at all between its terminals and the metal of the tank.
How a water heater element fails
- Lower element burnt out: hot water that runs out fast, because only the top of the tank is being heated
- Upper element burnt out: no hot water at all, since power is never passed down to the lower one
- Grounded element: the sheath has split and current leaks into the water, which trips the breaker or overheats the tank until the red reset button pops
- Scaled element: popping, hissing or sizzling as it heats, and slow recovery
- Dry-fired element: power switched on before the tank was full, which destroys a new element in seconds
Hard water in Halton and Hamilton is rough on the lower element in particular. Scale and sediment settle at the bottom of the tank until the element is buried, cannot shed its heat and burns out. The red button on the upper thermostat is the ECO, a high-limit cut-out that trips on overheating; if it trips again after one reset, the cause needs finding.
How elements are tested and what replacement costs
Testing is done with the breaker off and the circuit confirmed dead with a meter. The technician disconnects the wires and measures each element for resistance and for a short to ground, then checks both thermostats, since a failed thermostat looks identical from the tap. The full list of causes is in why is my water heater tripping the breaker.
Replacing a heating element runs $200–$400. The tank is drained below the element, the old one removed, a new one of the same voltage and wattage fitted with a fresh gasket, and the tank refilled and bled of air before the breaker goes back on. The diagnostic visit is $90–$150 and comes off the repair bill when the work goes ahead.
Element repair is worth it on a tank under about eight years old that is not leaking. On an older tank packed with sediment a new element often fails again, and a replacement electric tank at $1,200–$2,500 installed is the better use of the money.
What to do when an electric tank stops heating
Check the breaker first. If it has tripped more than once, or the red reset button will not stay in, leave the power off: 240 volts and water are no place for trial and error, and electrical work in Ontario falls under the Electrical Safety Authority's rules.
ZK Mechanical handles water heater element replacement and full water heater service for electric tanks. If short showers are the only symptom, a broken dip tube is the other suspect. See the HVAC glossary for more terms, or book a diagnostic visit.
Questions people ask about Water heater element
Can I replace just one element, or should both be done?
Only the failed one needs replacing. With the tank already drained, though, many owners choose to do both, along with the thermostats, once the heater is more than five or six years old, because the second element has seen the same water and the same scale. The replacement must match the voltage and wattage on the rating plate; a higher wattage can overload the circuit.
Why does my new element keep burning out?
Three causes account for most repeat failures. The tank was not completely full when power was restored, so the element fired dry. Sediment at the bottom has buried the lower element again. Or the element is the wrong voltage for the circuit. Flushing the tank and running a hot tap until the air is out before switching the breaker on prevents the first two.
Do gas water heaters have heating elements?
No. A gas tank heats with a burner under the tank and a flue up the middle, and a gas tankless heater uses a burner and a heat exchanger. Elements are found in electric tanks, electric tankless units and, as backup heat, in heat pump water heaters. If a gas heater has no hot water, look at the pilot, the thermocouple or the gas control instead.