Zodiac pool heater runs but water does not reach set temperature or heats very slowly.

Safety: Gas pressure and combustion adjustments should be performed by a qualified technician. Turn off power and gas before opening the heater.

• Verify setpoint and mode: Confirm the thermostat is set higher than current water temperature and that the correct mode (pool vs spa) is selected.
• Check run time and flow: Ensure the pump is running long enough and at sufficient flow for the heater's BTU rating and pool volume.
• Inspect burners: Remove the burner tray and check for rust, debris, or spider webs in the burners and orifices. Clean with compressed air; do not drill or enlarge orifices.
• Evaluate gas supply (pro): Have a licensed gas technician measure inlet and manifold pressure while the heater is firing and compare to Zodiac specifications. Correct any regulator or supply issues.
• Check for scaling: If the heater is older or used with hard water, internal scale may reduce heat transfer. Professional descaling or heat exchanger replacement may be required.