FIRST AND MOST IMPORTANT REMOVE THE PRESS FROM CURRENT!!!!
To check if the heatplate itself is working or if the phases are connected correctly to the heatplate you can measure the resistance on the heatplate connections of the SSR ! To get there,the cover simply has to be removed!
The resistance can be measured with a multimeter. The resistance of working and well connected heatplate has to be around 38 Ohms between the following possible combinations of the phases!