AL10 eror code on Hotpoint SDW80?

I have seen a few posts on this site on this topic but all of them (that I have seen) relate to the heater not working. Mine appears to be the opposite.

The dishwasher runs its rinse cycle with no problems but when it switches to the wash part of the programme you can hear the water boiling in the bottom of the machine but nothing else happens until the AL10 error code comes up and everything stops. I have removed the heater and it has no build up of limescale. A few posts suggest testing the heater with a multimeter, can anyone tell me how to do this with the heater off the machine?

Thanks