This will cover a little more in depth application of the heat sink paste that needs to be applied to the back of the triacs on the pcb board for the Bosch High KW electric tankless water heaters. When you are replacing the PCB control board on a Bosch electric tankless water heater for the high KW units such as the AE-115/WH17 or the AE-125/WH27 you want to make sure to apply the heat sink paste that comes with the new PCB board.
The heat sink paste will come in a small syringe type applicator and a small amount will need to be applied to the back of each triac. The triac's are the small black squares to the left of the PCB board labeled by the letter G in the picture below. The Bosch AE-115/WH17 will have 4 small black triac's to the left of the PCB board and the AE-125/WH27 will have 6 small black triacs to the left of the PCB board. There are service bulletins that show the PCB board replacement and heat sink application. Bosch Service bulletin EP-22 will show the PCB board replacement for all the newer high KW units with polymer modules. Bosch Service bulletin TWH-E2-22 will show the PCB board replacement for all the older high KW units with copper canisters.
For further questions or to purchase a new PCB control board please call GlobalTowne at 888-726-9752 or visit our website.