Zodiac pool heater shows E20; heater may not recognize water flow correctly even when pump is running.

Safety: Turn off power and isolate the heater from the plumbing (close valves) before removing any wet components. Relieve system pressure.

• Locate flow sensor: Identify the electronic flow sensor on the heater's water manifold or in-line plumbing, and trace its cable to the control board.
• Inspect and clean: Remove the sensor following Zodiac instructions. Check for debris, scale, or damage to the paddle or turbine (if present). Rinse with clean water; do not use harsh chemicals.
• Check orientation: Ensure the sensor is installed in the correct flow direction and orientation as marked on the body.
• Test wiring: Inspect the cable for cuts or kinks. Verify secure connection at the control board.
• Replace sensor: If cleaning and wiring checks do not resolve E20, install a new Zodiac-compatible flow sensor and test operation.