Heater runs but pool does not reach set temperature or heats very slowly

Safety: Normal operation checks can be done with the heater running; avoid touching hot surfaces.

• Verify setpoint and mode: Confirm the SunHeater is set to the correct body (pool vs spa) and that the temperature setpoint is above current water temperature.
• Use a pool cover: Uncovered pools lose large amounts of heat overnight. Use a solar or thermal cover to reduce heat loss and improve heating rate.
• Check gas supply: If other gas appliances struggle or flames appear weak, have a gas technician verify that the meter, regulator, and piping are sized correctly for the SunHeater's BTU rating.
• Inspect for scale: If the heater is several years old and used with hard water, the Heat Exchanger may be scaled, reducing efficiency. Have a professional perform a chemical descaling if necessary.
• Confirm pump speed: For variable-speed pumps, ensure the heater is programmed to run at the minimum flow rate recommended by SunHeater during heating cycles.