There is apparently no way around other than just doing a head clean(s). After several however the situation got worse with the light cyan channel, the light magentas and the light-light black all blocking up. According to Epson I should do 2 cleans in a row without printing the result, the 2nd clean is actually more rigourous that the 1st. Then leave overnight with the machine still switched on but resting. This apparently allows a minute quantity of ink/dye to leach out and this helps to soften the dried material in the blocked channels.
I did just that and printed the result this morning. There was some improvement, with only the light magenta channel still blank. The light cyan and the light-light black were partially printed so I did the same again and have left it switched on overnight. We will see what happens tomorrow.
I asked about cleaning cartridges or solvent which I used on my previous 1400 and apparently there are none available for the 3000