  We show that a five dimensional Universal Extra Dimension model, compactified
on a line segment, is consistently formulated even when the gauge symmetry is
broken solely by non-zero Dirichlet boundary conditions on a bulk Higgs field,
without any quartic interaction. We find that the longitudinal W+W- elastic
scattering amplitude, under the absence of the Higgs zero-mode, is unitarized
by exchange of infinite towers of KK Higgs bosons. Resultant amplitude scales
linearly with the scattering energy, exhibiting five dimensional nature. A
tree-level partial-wave unitarity condition is satisfied up to 6.7 (5.7) TeV
for the KK scale 430 (500) GeV, favored by the electroweak data within 90% CL.
