Pool heater will not start at all; display is blank and no lights are on.

Safety first: Use extreme caution when working around live electrical circuits. Turn off power at the main panel before opening the unit.

• Check breaker and disconnect: Verify that the dedicated breaker for the SPRSUN heater is ON and that any outdoor disconnect switch is in the ON position.
• Inspect wiring: With power off, open the electrical compartment and check for loose, burned, or disconnected wires at the terminal block.
• Measure voltage: If you are qualified, measure line voltage at the unit's terminals to confirm power is present.
• Internal fuses: Some SPRSUN models have internal fuses on the control board. Check and replace only with identical rated fuses.
• Board replacement: If correct voltage is present but the display remains dead, the main control PCB or its power supply section may have failed and should be replaced by a technician.