Unit displays HP and shuts down; pool water not heating and compressor stops shortly after startup.

Safety first: Turn off power at the disconnect and circuit breaker before opening the unit. Do not attempt to open the sealed refrigeration system yourself.

• Check water flow: Ensure all valves to and from the AquaCal heater are fully open. Clean the pool filter and backwash if applicable. Verify the pump is primed and running at normal pressure.
• Inspect the heat exchanger bypass: If there is an external bypass, confirm it is adjusted per AquaCal installation manual (usually partial bypass, not fully diverting flow). Too little flow can cause HP errors.
• Clean the evaporator coil: Remove the top or side panels as per AquaCal service instructions. Use a soft brush and low‑pressure water to rinse debris from the evaporator coil fins. Do not bend fins.
• Check airflow obstructions: Make sure there is at least the manufacturer‑specified clearance around the unit. Remove leaves, plastic, or covers blocking the fan discharge or coil intake.
• Reset and test: Restore power, clear the error (if the control allows), and restart the heater. Observe water flow and listen for normal compressor operation.
• If HP persists: The high‑pressure switch or refrigerant charge may be at fault. Contact a qualified AquaCal service technician to test the high‑pressure switch and measure system pressures.