Impurity injection in the JET ELMy H-mode regime has produced high confinement, quasi-steady state plasmas with densities close to the Greenwald density. However, at large Ar densities, a sudden loss of confinement is observed. A possible correlation between loss of confinement and the observed MHD phenomena both in the core and the edge of the plasma was considered. The degradation in confinement coincides with impurity profile peaking following the disappearance of sawtooth activity. Experiments were designed to understand the role of sawtooth crashes in re-distributing impurities. ICRF heating was used to maintain sawtooth activity and resulted in quasi-steady state, high performance plasmas with high Ar densities. At H97*fGWD~0.8 and high Ar injection rates, quasi-steady states which previously only lasted <τE, were now maintained for the duration of the heating (Δt~9τE). We conclude that sawtooth activity plays an important role in preventing impurity accumulation.