The ONLY way the doser will do this is if you have managed to get water onto the inner front board where the manual overide button connection ribbon cable sits.
easy to see - take the lid off, pop out the front board and you will see corrosion from salt water incursion. We had one last week, the client said the unit was above the fish tank, when we got it here you could have kept fish in the lower half of the unit
It had clearly gone swimming, not saying yours is that catastophic but the issue was the same.
This is the kind of damage you see with water being allowed to get into electrical devices
I
cant offer support here so please email me at
sales@aqua-digital.com with the outcome either way.
Parts are available for self replacement if you have damaged it.