Unit runs (fan and compressor on) but pool water does not heat or heats very slowly.

Safety first: Turn off power and pump before opening panels or plumbing.

• Verify run time: Heat pumps raise temperature slowly. Confirm the unit has run continuously for several hours and that the pool is covered to reduce heat loss.
• Check water flow: Ensure valves are open and filters are clean. Verify the heater’s inlet and outlet temperatures; a small temperature rise (2–5°F) across the heater is typical.
• Clean coils: Rinse the evaporator coil and clear debris from the fan area to improve performance.
• Inspect heat exchanger: If accessible, check for scale or debris in the water manifold. Flush per Heat Siphon instructions.
• Technician evaluation: If performance remains poor, a technician should check refrigerant charge and system pressures.