Hmm, interesting discovery, thanks for checking the code! FWITW though, I'm getting good readings on 4 MAX31855 breakout boards with this code. If this is a code issue, here is another MAX31855 library: GitHub - mcleng/MAX6675-Library: MAX6675 Arduino Library . I've tested it for Ryan's quad board: http://ryanjmclaughlin.com/wiki/Arduino_Thermocouple_Shield#Software .