Heater shows F1 and stops; may occur intermittently during operation.

Safety first: Turn off power before working on plumbing or wiring.

• Check water level: Ensure the pool water level is mid-skimmer; low water can draw air and cause flow interruptions.
• Inspect pump lid O-ring: A leaking lid can pull air. Clean and lubricate the O-ring and tighten the lid firmly.
• Clean filter: Backwash or clean cartridges to improve flow.
• Check flow switch wiring: Confirm the flow switch connectors are tight on the control board and at the switch body.

If F1 continues despite good flow, the flow switch may be worn and should be replaced.