Electric water heater element testing & replacement
Electric water heaters are a fundamental component in many residential and commercial applications. For professional plumbing contractors, servicing these units efficiently is critical to maintaining a strong reputation, ensuring profitability, and keeping customers satisfied. When an electric water heater stops producing hot water, or produces an insufficient amount, the first items to inspect are the water heater elements.
Why water heater elements fail
Identifying the root cause of water heater element failure can prevent recurring issues for your customers and save them from premature equipment failure.
Mineral buildup and scaling
The most common enemy of a water heater element is scale buildup. In areas with hard water, calcium and magnesium deposits naturally accumulate on the element over time. This calcification acts as an insulator, forcing the element to work harder and run hotter to reach the thermostat’s designated set point. Eventually, excessive heat causes the internal filament to fracture or short out. Recommending a water softener or scheduling regular tank flushing can help your customers avoid this issue and extend the life of their unit.
Dry firing
A dry fired water heater element is the result of power being turned on before the tank is completely full of water. Without water to absorb and dissipate the heat, the copper or stainless-steel sheath of the element can melt, warp, or burst. This is a costly and easily preventable mistake during installation or maintenance. Always ensure a steady flow of water from the highest hot water faucet in the home before energizing the breaker.
Electrical surges
Power surges, grid fluctuations, or lightning strikes can cause an immediate short within the heating element. The high voltage spike can sever the resistive wire inside, leaving an open circuit that completely halts the heating process.
Symptoms of a bad water heater element
Customers usually recognize a problem when their daily routine is disrupted by cold water. However, identifying which specific element is failing requires an understanding of the heating sequence.
Most residential tanks operate on a non-simultaneous sequence. The upper thermostat energizes the upper element to quickly heat the top portion of the tank. Once that water reaches the set temperature, power shifts to the lower thermostat, which energizes the lower element to heat the remainder of the tank.
No hot water: If there is absolutely no hot water, the water heater upper element or the upper thermostat is likely faulty. The system never satisfies the upper demand, meaning it never switches power to the lower element.
Not enough hot water: If customers get a short burst of hot water that quickly turns cold, the lower element water heater component is typically to blame. The top of the tank is hot, but the bulk of the water at the bottom remains unheated.
High electricity bills: A failing element coated in heavy scale is highly inefficient. If it takes twice as long to heat the water, it will reflect poorly on the customer's utility bill.
How to test water heater elements
Performing a proper diagnostic requires safety precautions and the right tools. Always start by turning off the power at the main breaker panel. Verify that the power is completely off using a multimeter before touching any wiring.
Checking for power
Remove the upper and lower access panels, peel back the insulation, and remove the plastic safety covers. Using your multimeter set to alternating current (AC) voltage, probe across the two screws on the thermostat to ensure zero voltage is present.
Conducting the ohm test
When apprentices learn how to check water heater element integrity, the most reliable method taught is measuring resistance (ohms).
Disconnect the two power wires attached to the face of the element. Leaving them connected can result in a false reading through the rest of the electrical circuit.
Set your multimeter to the ohms or resistance setting.
Place one probe on each of the element’s screw terminals.
A healthy replacement water heater element typically reads between 10 and 16 ohms, depending on its wattage rating.
If the multimeter reads open loop or infinite resistance, the internal filament may be broken and a water heater element replacement is required.
Checking for a ground short
Even if the element has the correct resistance, it could be shorted to the tank itself. Keep one probe on an element terminal and touch the other probe to the bare metal tank body. If the meter shows continuity, the element is shorted and must be replaced immediately to prevent electrical hazards.
Replacing a water heater element
Once you have diagnosed a failure, the next step is knowing how to change water heater element parts safely.
Are water heater elements universal?
While many elements look similar on the shelf, they vary significantly in wattage, voltage, length, and material composition. You must exactly match the electrical ratings of the original element to avoid overloading the wiring or instantly burning out the new part.
When choosing between OEM vs. aftermarket elements, aftermarket parts are widely used and perfectly acceptable as long as the specs match. In some cases, they even offer material upgrades for hard water environments. However, OEM parts are recommended if the water heater is still under warranty, to avoid voiding the coverage, or if the unit requires a proprietary mounting flange.
Low-density vs. high-density water heater elements
When referring to water heater elements, density specifies the amount of wattage per square inch of surface area on the element itself.
High-density elements feature a single, narrow U-shaped tube. Because they output a high amount of wattage into a smaller surface area, they run exceptionally hot. This intense heat causes them to quickly attract limescale in hard water, leading to lower efficiency and a shorter lifespan over time.
Low-density elements double back on themselves to create a longer, folded double-loop shape. This larger surface area distributes the heat more evenly. Although they are a premium part that costs more upfront, low-density elements attract scale much slower, operate more quietly, and boast a significantly longer useful life.
Regardless of whether you choose a high or low-density option, ensure the replacement element shares the same wattage rating and mounting style as the original.
Screw-in vs. flange-style water heater elements
When selecting a replacement, you must also identify how the element mounts to the water heater tank. The most popular style used in modern residential applications is the screw-in version, which features a threaded hex head that screws directly into the tank. However, a four-bolt flange style is also very common, particularly on older units or specific commercial models.
A flange-style element is secured to the tank using four bolts and a separate gasket. Because these mounting styles are not interchangeable, it is critical to verify the physical configuration of the original element before sourcing a replacement.
What size is a water heater element socket?
Having the correct tool prevents severe damage to the new element and the tank. The standard size for screw-in residential elements is 1-1/2 inches. Attempting to use a standard adjustable wrench or locking pliers can easily strip the hex head. A purpose-built element socket tool ensures a secure, flush fit without slipping.
How to remove a water heater element
The cost of a replacement element is generally low, making this a highly profitable service call for contractors. Prices vary based on material and whether it is a standard or high-watt density model. Investing in a durable, high-quality replacement ensures longevity and minimizes frustrating callbacks.
Follow these steps for a safe and effective replacement:
Drain the tank: After verifying the power is off, attach a heavy-duty garden hose to the drain valve. Open a hot water faucet inside the house to relieve vacuum pressure, then open the drain valve. You only need to drain the water below the level of the element being replaced, but draining the whole tank helps remove settled sediment.
Remove the old element: Disconnect the power wires. Use your 1-1/2 inch socket to carefully turn the element counterclockwise. Have a rag or bucket ready, as residual water may spill from the opening.
Clean the threads: Inspect the internal tank threads. Use a small wire brush to remove any scale, debris, or rust. This ensures the rubber O-ring gasket on the new element seats perfectly.
Install the new element: Insert the new element and hand-tighten it clockwise to avoid cross-threading. Once hand-tight, snug it down with the socket wrench. Do not overtighten, as this can deform the gasket and cause immediate leaks.
Refill and bleed: Close the drain valve. Turn the cold water supply back on. Leave the hot water faucet open inside the home until a steady, bubble-free stream of water flows. This step is mandatory to prevent dry firing the new element.
Reconnect and power up: Reconnect the two power wires to the element terminals. Replace the safety covers, insulation, and access panels. Turn the breaker back on and test the water temperature at a faucet after about an hour.
Equip your team for success
By utilizing the correct diagnostic techniques, keeping essential water heater parts in your truck, and educating customers on preventative maintenance, you can ensure efficient and profitable service calls. Shop Ferguson for access to top water heater brands and all the parts and accessories to keep your jobs on schedule.