Display shows E10; unit does not start heating even though pump is running.

Safety first: Turn off power and close valves if you will open any part of the plumbing system.

• Confirm pump operation: Ensure the pool circulation pump is running and primed. Check for air in the pump basket.
• Clean filtration system: Backwash or clean the pool filter, empty skimmer and pump baskets, and remove any obstructions in suction lines.
• Check valves: Verify that inlet and outlet valves to the SPRSUN heater are fully open and that any bypass valve is adjusted according to the installation manual (usually mostly closed so most flow passes through the heater).
• Inspect flow switch: Locate the flow switch or flow sensor on the heater's water circuit. Check wiring connections and ensure the arrow on the body points in the direction of flow.
• Test and replace: If good flow is present and E10 remains, the flow switch may be stuck or defective and should be replaced with a compatible SPRSUN flow switch or flow sensor.