F5 error and no hot water on electric Giant water heater with digital control

Safety first: Turn off the breaker supplying the water heater and verify power is off with a meter. Water inside may be hot.

• Access upper element: Remove the upper access panel and insulation to expose the upper thermostat and element on the Giant heater.
• Check ECO reset: Press the red reset button on the upper thermostat until it clicks.
• Inspect wiring: Look for burned or loose wires at the element and thermostat. Tighten connections and replace any damaged wire using proper high‑temperature wire.
• Test element: Disconnect the wires from the upper element and measure resistance across the terminals. A typical 4500 W/240 V element reads around 12–13 Ω. If open, replace the Giant upper heating element.
• Restore power and test: After reassembly, restore power and check for normal operation. If F5 persists, the control board or thermostat may be faulty and should be serviced by a technician.