WiremanWireman · Electric water heater not heating: troubleshooting for electricians · 2023 NEC ·
Electric water heater not heating
Power, the high-limit reset, then each element and thermostat.
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How it works
Most residential electric water heaters have two elements that never run at the same time. The upper thermostat powers the upper element first; when the top of the tank is hot, it switches power down to the lower element. So no hot water usually means the top side, and hot water that runs out fast usually means the bottom.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What’s happening?
- No hot water at allTest: Check power at the upper thermostatExpect: About 240 V.
- 0 VNo power to the water heater
- 240 VWith power off, press the red reset button above the upper thermostat. Did it click?
- It clicked and heat came backThe high-limit tripped
- No click, or still no heatTest: Test the upper elementExpect: About R = V² ÷ W: 12.8 Ω for 4500 W at 240 V, 10.5 Ω for 5500 W. Open (OL) to the tank.
- OL across the terminalsBurned-out element
- Reads to the tankElement shorted to the tank
- Normal resistance, open to tankUpper thermostat
- Lukewarm, or runs out quicklyTest: Test the lower elementExpect: 10–17 Ω depending on wattage, and open to the tank.
- OL across the terminalsBurned-out element
- Reads to the tankElement shorted to the tank
- NormalLower thermostat, or the upper isn’t switching power down
- No hot water at allTest: Check power at the upper thermostatExpect: About 240 V.