Heater displays E03 and will not start; blower may not run

Safety: Turn off power to the SunHeater pool heater before opening the cabinet. Water-side checks can be done with gas off but pump running.

• Verify pump operation: Ensure the pool circulation pump is running and primed. Check for air in the pump basket and correct any suction leaks.
• Check filter and valves: Backwash or clean the pool filter. Confirm all valves leading to and from the heater are fully open, including any bypass valves around the heater.
• Inspect the water pressure switch: Locate the Water Pressure Switch on the inlet manifold. Remove its wires and check continuity with a multimeter while the pump is running. It should read closed (continuity) when there is adequate flow. If it remains open, adjust the switch (if adjustable) or replace it.
• Check for internal obstructions: With the pump off and valves closed, remove the inlet and outlet unions at the heater. Inspect for debris lodged in the header or heat exchanger inlet.
• Reset and test: Restore flow, power, and call for heat. If E03 persists despite good flow and a known-good pressure switch, the main control board may not be reading the switch correctly and should be evaluated by a technician.