You need to reset the purge counter. (How many times it has cleaned)
Here's how...
1. Press 'menu', 'mono start' then 'menu' one by one...
2. Press the arrow up or down to go to 'maintenance 80'.
3.
Press 'mono start' several times to go to 'Purge'. Finding the PURGE
will show some numeric value which is I assume the number of times the
printer had cleaned.
4. Press 'arrow up' key and scroll for number
"2" then press "set". Do the same for numbers 7, 8 and 3. After you
have entered this combination, the purge numeric value will be reseted
to 00000.
Here's a link to the Support Site for your printer where you can download the User's Manual.