What it is
The troubleshooting tree for "no hot water" on a dual-element electric tank. Electric units fail in predictable ways, and the symptom often tells you exactly which element to check before you ever pull a meter. The whole job is: confirm power is reaching the elements, find which thermostat/element link is broken, and don't reset a tripped ECO without finding what tripped it. Lock out and verify zero volts before touching anything — it's 240V.
How it works
A standard electric tank heats top-down and non-simultaneous — only one element runs at a time. The upper thermostat heats the upper element first, then transfers power to the lower thermostat/element. An ECO high-limit on the upper thermostat kills everything if the water runs away hot. So "no hot water at all" usually means power isn't getting through at the top (breaker, ECO, upper thermostat, upper element), while "lukewarm / runs out fast" usually means the lower element is dead (you get the top third hot, then nothing). Knowing that split tells you where to meter first.
In the field
Work it in order, power off until you're ready to read voltage:
- Confirm the complaint and the easy stuff. Stone cold everywhere, or lukewarm/short supply? Confirm the breaker is on and not tripped (a tripped breaker is often a grounded element — note that for later). Confirm the disconnect is on.
- Pull the upper access panel, fold back insulation, and find the ECO reset button (red button on the upper thermostat). If it's tripped, press it — but understand a tripped ECO means the water overheated, so you'll come back to find the cause (grounded element or welded thermostat).
- Verify power into the heater. With power on and meter in hand (careful — live 240V), confirm 240V coming in to the ECO/upper thermostat. No incoming power → breaker/disconnect/wiring upstream.
- Use the top-down logic to test. On a cold tank, the upper element should be energized (read ~240V across it). If 240V is present but it's not heating, the upper element is open — ohm it (power off): good 4500W element ≈ 12–13 Ω; OL = open/burned out.
- Find a dead lower element (the lukewarm case). Once the top is satisfied, power transfers to the lower element. If the customer gets a little hot water then cold, the lower element is the usual suspect. Power off, ohm the lower element — OL means it's open. This is the single most common electric no-/low-hot-water failure.
- Ground/short check on every element you test. One lead on an element terminal, the other on the bare tank — should be OL. Any continuity = grounded element (shorted to sheath). That's what trips breakers and ECOs. Replace it.
- Thermostat check. If an element reads good (12 Ω, no ground) but gets no voltage when its part of the tank is cold, the thermostat feeding it isn't passing power — replace the thermostat. Make sure the new one seats flat against the tank.
Normal values & targets
- Element resistance (240V): 3500W ≈ 16 Ω, 4500W ≈ 12–13 Ω, 5500W ≈ 10 Ω. OL = open; near-zero = shorted.
- Element-to-tank: OL (any continuity = grounded element).
- Voltage at the called element: ~240V (upper on a cold tank, lower after the top is hot — non-simultaneous).
- ECO trip: ~170–180°F, manual reset; it tripping means a real overheat occurred.
- Recovery: single 4500W element ≈ 20–21 GPH at 90°F rise — slow, so "runs out" can be demand outrunning recovery.
- Setpoint: typ. 120°F; both thermostats set the same.
Common faults & what they mean
- Stone cold everywhere → tripped breaker, tripped ECO, upper element/thermostat open, or no incoming power. Work breaker → ECO → upper in order.
- Lukewarm, runs out fast → lower element open (top heats, bottom doesn't). Most common electric failure.
- Breaker or ECO keeps tripping → grounded element (check terminal-to-tank). Reset/replace only after finding the ground fault.
- Element reads good but no voltage to it (that zone cold) → thermostat not passing power; replace thermostat, seat it flat.
- New element failed within days → dry-fired (energized before the tank was full). Always fill and bleed air before powering up.
- No hot water right after install → check it was filled, breaker on, and both elements get power in sequence; confirm wiring.
Tech tips & gotchas
- Lock out and verify zero volts before touching elements. 240V will hurt you. Read voltage steps live only when you have to, with care.
- The lukewarm symptom is a gift — it's almost always the lower element. Top-down heating means a dead lower element gives a slug of hot then cold. Go straight to ohming the lower element.
- Always check elements to ground, not just terminal-to-terminal. A grounded element can read a perfect 12 Ω across its terminals and still be the thing tripping the breaker/ECO. Skipping the ground check gets the wrong part replaced.
- A tripped ECO is a symptom. Don't just reset it and leave. Something overheated the water — find the grounded element or welded thermostat, or you'll be back.
- Non-simultaneous confuses people: a stone-cold tank with 0V at the lower element is normal — power's at the upper until the top's satisfied. Don't condemn the lower thermostat for that.
- Fill and bleed before energizing any new element. Dry-firing burns an element out in seconds and is the top "new part failed instantly" callback.
Safety / code notes
- 240V appliance — de-energize and verify zero volts before servicing elements; confirm the equipment ground is intact, especially after replacing a grounded element (electrical code grounding/bonding).
- The ECO is a safety, not a control — never jumper it to keep a unit running. If it keeps tripping, fix the overheat cause.
- Confirm the T&P valve and discharge are correct on every unit (IPC water-heater/relief provisions); a tank that overheated (tripped the ECO) may also have stressed the T&P.
- If a thermostat repeatedly welds or an element repeatedly grounds, look for an underlying cause (sediment, scale, wrong element type, or a control issue) rather than just swapping parts.