Display is on but compressor and fan never start; unit always shows standby even when heat is requested.

Safety first: Ensure safe access to the control panel; no need to open electrical compartments for basic checks.

• Check operating mode: Confirm the SPRSUN heater is set to HEAT (not COOL or OFF) and that any timers are not preventing operation.
• Verify setpoint: Make sure the desired pool temperature is set higher than the current water temperature displayed.
• External controls: If connected to an external controller or BMS, ensure it is calling for heat and not in an off/lockout state.
• Sensor sanity check: Compare the displayed water temperature to an independent thermometer. If the reading is much higher, a sensor may be faulty and should be replaced.