Creda washing machine trips the RCD circuit breaker?

My Creda 1000 Supaspeed washing machine model 17086 trips the RCD circuit breaker every time the water reaches the fill level (I hear the pressure switch switching). The motor works fine as I can get it to spin once the water level drops below the fill level. I've traced the wire that has its contact made by the pressure switch to the heater element. Does this mean that the heater is shorting to earth? The trip doesn't go if I disconnect the wire to the heater and fill the machine, but then it doesn't stop filling. Is the fill stopped when the pressure switch reaches the second contact point ?