Unit powers on but quickly shuts down with “HP” on the display; pool water is not heating and the compressor does not stay running.

Safety first: Turn off all power to the Heat Siphon pool heater at the breaker and disconnect any service disconnect before opening panels. Do not work on the refrigerant circuit unless you are EPA-certified.

• Check water flow: Ensure the pool pump is running at full prime. Verify all valves before and after the heater are fully open. Clean the pool filter and pump basket to restore proper flow.
• Inspect the condenser coil (air coil): Remove leaves, grass, and debris from the coil fins. Use a garden hose with low pressure to rinse from inside out. Do not bend fins.
• Verify fan operation: Restore power and briefly run the unit. Confirm the fan starts immediately when the compressor runs. If the fan is not running, shut power off and investigate the fan motor and capacitor.
• Reset the unit: After correcting flow and airflow issues, power the unit off for 5 minutes, then back on. Clear any lockout by cycling power and recheck operation.
• If HP returns quickly: The high‑pressure switch or refrigerant charge may be at fault. Do not bypass the switch. Contact a qualified Heat Siphon technician to test the high‑pressure switch and system pressures.