Hi Coccinelle,
I think that you will find that most printer cleaning programs waste a hell of a lot of ink as it cleans all colours repeatedly whether they need cleaning or not.
Make a small .doc file with a single line of capital letters of each colour, ie., black, yellow, cyan and magenta then print it out.
If a certain line of colour has a white or pale streak running through it, then simply print half an A4 page .doc file of that particular colour to see if it clears itself.
If it doesn't clear then repeat the saucer of hot water (about 1/4" ) as necessary and then try the coloured .doc file printing again.
Continuing to print after a fault (white line) appears in the printing could cause that particular nozzle of the print head to burn out due to the surrounding ink not keeping the heating element cool, consequently that particular nozzle cannot be repaired. Therefore stop printing as soon as the fault appears and try to get the ink flowing again
I always refill my cartridges when they are still half full, thus avoiding any fault lines appearing in the first place.
Hope this helps.