Developed and tested probes based on the gradient heat flux sensors to measure the combustion chambers of power boilers. Developed a technique and carried out calibration of probes on a physical model of the furnace gas proof shield, held the endurance tests of the probes in multicyclic thermal stress. Developed methods of mounting the probes without disturbing the integrityof the boiler water-steam tract. Methodological foundations of the gradient heat flux measurement in combustion chambers are laid. Developed and successfully tested heat flux measuring system based on the probes in the boiler P-49 with supercritical pressure; there are results of industrial tests.