What does it mean that Huixi water heater can't produce hot water ee?

The alphanumeric ee displayed on the screen is a fault code to remind you of the problem. As for the specific problem, because each brand is different, you can look at the product manual that comes with the brand when you buy it to find out what the problem is. Or directly call the brand's after-sales service hotline, say specific problems, and let them arrange people to repair them in time.