  Extending the Standard Model by adding a scalar field transforming as a
septet under $SU(2)_L$ preserves the $\rho$ parameter at tree level and can
satisfy experimental constraints on the electroweak parameters $S$ and $T$.
This work presents the first fully general phenomenological study of such an
extension. We examine constraints on the septet model couplings based on
electroweak and Higgs observables, and use LHC searches for new physics to
bound the mass of the septet to be above $\sim 400$ GeV at a $95\%$ CL.
