Unit displays E03 and will not heat; compressor does not start or stops shortly after starting.

Safety first: Turn off all power to the SPRSUN pool heater. High voltage is present inside; if you are not comfortable with electrical testing, contact a technician.

• Check supply voltage: Verify that the breaker feeding the heater matches the unit's rated voltage (e.g., 230V single-phase). Look for tripped breakers or burned lugs at the disconnect.
• Inspect wiring: With power off, remove the electrical cover and visually inspect the compressor contactor, terminal block, and wiring harness for burnt or loose connections. Tighten loose screws and replace any melted components.
• Allow compressor to cool: If the unit has been short-cycling, wait 30–60 minutes for the internal overload to reset, then restore power and attempt a restart.
• Do not repeatedly reset: If E03 returns immediately, the compressor may be drawing excessive current. Repeated resets can cause further damage.
• Call a professional: A qualified technician should measure compressor winding resistance, check start components (if applicable), and test the inverter PCB or contactor.