Miele Salt Problem

First attempt on a forum so here goes. I have a 5 year old Miele G691 I think the model number is right it has lots of buttons on the front. It has been perfect until recently. I have not changed from salt/finish liguid/finish rinse aid but it has started demanding salt every other wash, so 3 times per week. I fill the salt reserve and hey presto 2 washes later it wants more. There is none left in the reserve.

It also leaves fast quantities of white build-up on everthing. It scrubs off with warm water and according to my husband tastes salty.

I have made sure the salt reserve top is screwed on properly and pre-washed to remaove any loose salt granules that may have been left in the main dishwasher. There are no food deposits on the plates etc just this white stuff, presumable salt.

Is this a known problem with 5 year old Miele dishwashers?

Any suggestions please.