Nibe PCBA SMO S, part number 818956 is a replacement electronic control board used in NIBE SMO S‑series controllers. 

Details
•     Name: NIBE PCBA SMO S (sometimes listed as PCBA SMO S RES.D)
•     Part number: 818956
•     Function: Replacement printed circuit board (PCB) for the NIBE SMO S / SMO S40 control module
•     Used in: NIBE air‑to‑water heat pump systems that use the SMO S controller