This sounds like the float or sensor has become stuck or failed.
Please first start by checking the reservoir is correctly install at the rear, then check the float on the tank is moving freely with the water level (see image here showing the float), if it is stuck and you cant free it, you can look to purchase a replacement tank here, but you will need to make sure you buy the right tank for your model.
If the float is working freely, then the fault is most likely to be the sensor inside the machine itself. These sensors are not available on order, and the only option is to take the unit to a service centre.
If you provide me with your postcode I can advise of your nearest service centre.Regards
Unfortunately there are no service centres in you area, so you will need to send it to post it to the central service centre.
If you would like to arrange the repair Bosch do not charge to inspect the unit, but if the unit is 2 or more years old, they require you to cover the postal costs for sending it to them. They will then give you a quote for repair, and at that point you can chose to accept the repair based on the quote they give you (which I would think would be around £50 including parts), or they can return it back to you free of charge.
Should they be unable to repair it they will offer you the option for a recondition unit or the option to buy a new unit at a discounted price.
To book it in for repair please take note of the EN-r and FD number which can be found on a small plate, once you remove the reservoir, please call Bosch on***********and select option 1.
PS: If your posting it, I suggest you use the website here, it is vastly cheaper than using the Post Office.
I havent heard from you in a few days, and wanted to understand if I can be of any further assistance, and ask if you can rate the service received.