Abstract: A boiler protection tube assembly having an inner ceramic sleeve, a ceramic block and an outer ceramic sleeve. The inner ceramic sleeve is of a high-strength, heat resistant ceramic material with at least moderate thermal shock resistance. The outer ceramic sleeve is of a heat resistant, insulating ceramic fiber and extends around the outer sleeve along its length. The inner and outer sleeve are insertable through a hole which extends through the ceramic block into an end of a condenser tube of a tube sheet boiler. The outer ceramic sleeve reduces heat flow between the inner ceramic sleeve and both of the ceramic block and the condenser tube. The ceramic block has a plurality of side faces generally perpendicular to the inner and outer faces to enable the blocks to be installed with side faces adjacent to corresponding side faces of adjacent blocks.