it might not be the cooker, you might need to check the wall socket wireing to see that everything is tight, and there is no movement of any wires in there, and check the main power lead going into the cooker, that all wires are tight, and the 3 wires at the element are also tight, you will be checking all of this with (ALL THE POWER OFF), or the roast wont be the only thing cooking....
m
September 2012