The project was done in order to investigate if thermocouples can be used to measure the temperature according to the EU directive about waste combustion. Measurements were done in two boilers, one bubbling fluidized bed and one grate boiler. The results showed that the boundary layer varies in time and space in the boilers. This indicates that the use thermocouples in this application demands several measuring points. The thermocouple measurements were parallel to the suction pyrometer measurements which gives possibilities to correct fore the measuring error.