Heater shuts down with E04 after running briefly; display may show rising temperature quickly

Safety: Turn off power and gas. Allow the heater to cool completely before touching internal components.

• Check water flow: Ensure the pool pump is running at the correct speed and that the filter is clean. Verify that all valves to and from the SunHeater are fully open.
• Inspect high limit switches: Locate the High Limit Switches on the outlet header. Remove the wires and test each switch for continuity at room temperature. A good switch should read closed. If open, replace the faulty high limit switch.
• Look for scale or blockage: If E04 recurs with good flow and new switches, the heat exchanger may be scaled or partially blocked, causing localized overheating. Inspect the inlet/outlet for mineral buildup. Professional descaling of the Copper Heat Exchanger may be required.
• Bleed air from system: If your plumbing has high points, air can trap and reduce flow. Use any installed air bleeders or briefly loosen a union (with pump off) to purge trapped air, then retighten.
• Test operation: Restore power and gas, then monitor temperature rise. If the outlet temperature spikes rapidly before E04, shut down and schedule a professional inspection.