The invention relates to a method for de-scaling a radiant syngas cooler. The method comprises adding de-scaling additives into the radiant syngas cooler, wherein the de-scaling additives comprise at least one of fire proof materials, copper compounds and vermiculite; depositing ingredient gas phases capable of forming scales in the fire proof materials, wherein the copper compounds react with at least part of ingredients capable of forming the scales to be expanded and/or with the vermiculite in the scales.