The ITER limiter first wall cooling system, which consists of a large number of small channels with common inlet and outlet headers, is expected to be subjected to extremely high fluxes during startup and shutdown. The potential for parallel channel two phase flow instability is examined. At the specified flow rate, the first wall system should be stable, but this conclusion depends critically on the ability to accurately predict the heat load profile. The analysis is performed assuming that all channels are subjected to the same heat loading. The situation in which the channels are subjected to different heat fluxes calls for further examination.