GE heat pump water heater shows F4 and the compressor will not run.

Safety: Turn OFF power at the breaker. Components near the compressor can be hot; allow time to cool.

Steps to address F4:

• Locate discharge sensor: Find the sensor clipped to the small-diameter copper line leaving the compressor (discharge line).
• Inspect attachment: Ensure the sensor is firmly clamped and insulated as designed. A loose sensor can cause incorrect readings.
• Check wiring: Look for melted insulation or brittle wires near the hot discharge line. Repair or replace damaged harness sections.
• Test sensor: Disconnect and measure resistance with a multimeter. Compare to GE’s chart for the approximate line temperature. Replace if open/shorted or out of range.
• Control board check: If the sensor is good, inspect the control board connector and traces. Reseat the plug and look for discoloration.
• Power up and test: Restore power and see if F4 clears. If not, the control board may require replacement.

Note: Persistent high discharge temperature without a sensor fault may indicate a sealed system problem and should be handled by an EPA-certified technician.