My Indesit WIE1375 is showing F-08?

My Indesit washer is showing F-08 and tries to pump water out when the washer is off or mid cycle or after a cycle has finished it will lock the door again and display F-08 (?) The Indesit website suggests this is to do with the heater but if so why would it do it when the washer isn't even switched on. I have had a local engineer out twice who cannot figure out what the fault is but suggests a new control board which will be expensive. Can anyone help please?