Woken this morning, by Av complaining the downstairs toilet, wouldn't flush, because the cistern wasn't filling with water - she'd had to use a bucket.....
By 11am, I was just about awake enough to go take a look. The little plastic float valve, was catching on top of the flush. Somehow, the plastic flush valve (beginning with a 'D') had managed to rotate several degrees, enough to place itself under the float. The water continued to drip from the fill valve, even with the local isolator off. I managed to work out it was passing through TMV, so isolated at the local HW isolator too. Bailed out the cistern, removed the flush, just a plastic peg holding it, rotated flush pipe, and refitted the flush. Water back on - tested and working.
I still don't know, how the flush managed to rotate in the cistern, it was quite tight in there?