System for cleaning boilers, preferably lignite boilers comprising: - at least one cleaning device, for cleaning the boiler internally, comprising a spray head with a cavity and a water supply connection; - a suspension means for each of the cleaning devices, for keeping the cleaning device suspended at the top of the boiler and adjusting the height position of the cleaning device relative to the top of the boiler, wherein the suspension means is suitable for being coupled with the cleaning device with one end, and wherein the suspension means is coupled with another side to the top of the boiler; - a lifting device for each of the suspension means, for raising and lowering the suspension means, in particular raising and lowering the cleaning device; and - a water supply means adapted to be coupled to the water supply connection of the cleaning devices for supplying high pressure water to the cleaning devices; wherein the system further comprises a controller suitable for controlling the lifting devices, wherein the height position of the suspension means is controlled, and wherein the controller monitors the cleaning of the boiler, the spray head comprising a plurality of openings, and the openings comprising a channel extending from the cavity of the spray head to the surface of the spray head, the cleaning device comprising a longitudinal axis, characterized in, that at least one of the openings, and preferably at least two, is an offset opening, which extends substantially perpendicularly with respect to the longitudinal axis of the cleaning device with a deviation of up to 20°, preferably of up to 15°, more preferably of up to 10°, wherein a perpendicular projection of the channel of the offset opening on a plane perpendicular to a longitudinal direction has an offset with respect to said longitudinal axis. - at least one cleaning device, for cleaning the boiler internally, comprising a spray head with a cavity and a water supply connection; - a suspension means for each of the cleaning devices, for keeping the cleaning device suspended at the top of the boiler and adjusting the height position of the cleaning device relative to the top of the boiler, wherein the suspension means is suitable for being coupled with the cleaning device with one end, and wherein the suspension means is coupled with another side to the top of the boiler; - a lifting device for each of the suspension means, for raising and lowering the suspension means, in particular raising and lowering the cleaning device; and - a water supply means adapted to be coupled to the water supply connection of the cleaning devices for supplying high pressure water to the cleaning devices; wherein the system further comprises a controller suitable for controlling the lifting devices, wherein the height position of the suspension means is controlled, and wherein the controller monitors the cleaning of the boiler, the spray head comprising a plurality of openings, and the openings comprising a channel extending from the cavity of the spray head to the surface of the spray head, the cleaning device comprising a longitudinal axis, characterized in, that at least one of the openings, and preferably at least two, is an offset opening, which extends substantially perpendicularly with respect to the longitudinal axis of the cleaning device with a deviation of up to 20°, preferably of up to 15°, more preferably of up to 10°, wherein a perpendicular projection of the channel of the offset opening on a plane perpendicular to a longitudinal direction has an offset with respect to said longitudinal axis.