Sorted.

My printer has not been printing properly since it was moved while decorating. I finally spent an evening sorting it out.

I have a continuous ink system, occasionally there is a build up of "foam" within the ink cartridges, that is what had happened, once cleared all was well again.

If you use the manufacturers cartridges, they run out of ink before the foaming is a problem, one of the reasons they don't make them too big!