Inhibition of contamination of the plasma core in JET by edge impurities during high power heating of deuterium plasmas in limiter configuration using fueling is demonstrated. By injecting deuterium gas during heating, in the presence of very much larger recycling deuterium flux, a reduction of more than factor two was effected in nz (0)/F,z the ratio of central impurity density to impurity influx at the plasma edge. The reduction in nz(0) was obtained without much effect on peak electron temperature and density. Reduction of plasma contamination by gas fueling was observed also when hot spots formed on the limiter, a condition that without simultaneous gas fueling culminated in runaway plasma contamination. Detailed analysis of the experiments is undertaken with the purpose of identifying the processes by which plasma contamination was inhibited, employing standard limiter plasma contamination modelling. Processes which might produce the observed impurity inhibiting effects of gas injection include (a) reduction in impurity production at the limiter, (b) increase in impurity screening in the scrape-off layer, (c) increase in radial impurity transport at the plasma edge, (d) increase in average deuteron flow velocity to the limiter along the scrape-off layer. These are examined in detail using the Monte Carlo limiter impurity transport code LIM. Bearing in mind that uncertainties exist both in the choice of appropriate modelling assumptions to be used and also in measurement of required edge plasma parameters, impurity modelling of changes in nz(0)/Fzby factor two is at the limit of present capability. However, comparison between LIM code simulations and measurements of plasma impurity content indicate that the standard limiter plasma contamination model may not be adequate and that other processes need to be added in order to be able to describe the experiments in JET.