The heater runs but the pool does not reach the set temperature or heats very slowly.

Safety first: Ensure the heater is operating normally without error codes before troubleshooting performance.

• Cover the pool: Use a solar or thermal cover to reduce heat loss, especially overnight and in windy conditions.
• Check setpoint: Confirm the heater set temperature is higher than the current water temperature and that the mode (pool/spa) is correct.
• Verify run time: Ensure the circulation pump and heater are running long enough each day to raise the temperature; large pools may require many hours.
• Inspect for bypass: Make sure any AstralPool bypass valve is not diverting too much water around the heater.

If heating remains inadequate, have a technician verify gas pressure (for gas heaters) or refrigerant charge (for heat pumps) and confirm the heater is correctly sized.