John, The protective circuit wont turn off the oven until you exceed approx. 40-45ua on the ion pump reading. Hard to say if you will reach end of life from other factors first given that it is a high performance unit. They have a much shorter life than a standard tube. It is sometimes possible to clear the whisker from the ion pump and return to a normal current value. Corby Dawson ____________________________________________________________ Click now and enjoy a fantastic vacation in the wine country. http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTHhwhGyaFV657WfVW3Iqi5Cuy0Tu5xURbu1lXbnh3tlLQnnEK1ShC/