Heater starts and stops frequently (short cycling) without reaching the desired pool temperature.

Safety first: Turn off power before moving sensors or opening the heater.

• Check sensor location: Ensure the water temperature sensor is sensing mixed pool water, not water directly from the heater outlet or spa return.
• Pump speed settings: If using a variable-speed pump, avoid very low speeds while the heater is running. Program a higher speed during heating cycles.
• Inspect internal bypass: A stuck bypass can cause rapid temperature changes at the sensor. Service or replace the bypass valve if needed.
• Thermostat setting: Avoid setting the thermostat only 1–2°F above current water temperature; use a larger differential to reduce cycling.