The message OH means Overheating and occurs when the water temperature is above 42 degrees. This can also happen if the temperature sensor is malfunctioning, which is still unusual. If the sensor is faulty, it must be replaced.
When the display shows OH, the system cannot be restarted with the ON/OFF button, only from the main breaker. If it is still in OH mode after restart, it will not do anything but show OH on the display.
If the water temperature is too hot, it must be decreased. For example, by adding cold water or letting it cool down with the lid off. If the sensor is faulty, it must be replaced.
Also check that the system is set to automatic filtration mode (button with green drop) and not to manual mode (red drop) which means that the pump runs 24/7 and heats the water without the temperature setting and sensor being able to extert any control.
Error message E1 and E0
If E1 is displayed on the panel, there is a fault in the contact with the temperature sensor. In this case, disconnect the connector between the sensor wire "TEMP" and the control system. Clean the "connecting pins" and use e.g. CRC or other contact spray and reconnect.
If E0 is displayed on the panel, then the temperature sensor is short-circuited. In this case, the sensor must be replaced. The circulation pump and heating are not activated in these situations. Error message E0 can also occur if there is a fault in the connector to the sensor, it could be a fault with the cable or the control board.
First try disconnecting the sensor from the black wire marked "TEMP" and cleaning the contact points, also use contact spray. If that does not help, turn off the power and open the cover of the control box:
Locate the 12V control board on the top right and check the connections to make sure they are properly pressed down.
If it looks like the picture, E0 will appear on the display. Correct by pressing down the connector.