The water is so hot that the first time I turn on the water heater, I got scalded.

This could happen from 2 reasons:

1. Problem: There was hot water in the boiler before turning on the water.

Cause: The interval is too small.

Solution: Turn down water volume

2. Problem: Heater is always on.

Cause: Broken PCB, Broken Heater, or Ground.

Solution: contact service center