A high-temperature module for electrolysis of water with improved operational safety, in which steam containing at most 1% hydrogen can be made to flow simultaneously in each cathode and in each anode, as a draining gas, of a stack of cells. The stack of cells is housed in a sealed case and a mechanism for clamping by compression of the stack is included. The risks of leaks likely to cause impairments of efficiency and breakages of all or part of a stack EHT electrolyzer are reduced, while a high level of efficiency is provided due to the fact that satisfactory electrical conduction is maintained by compression of the stack.