Thanks for your comments on the ball valve stopping, running for a short time then stopping again etc ( cycling ). I accept its not the most interesting subject but it is a problem to solve, its not a new site ( 30 years installed ) and has never had a problem before, the link pipe is clear and...
I have a double tank in my loft feeding cold gravity taps and and hot cylinder. I have replaced the side entry ball cock ( twice ) and it still cycles on fill.
It does not seem to do it when its empties for a bath but the upstairs tap and bathroom loo ( fed from the tank ) cause it to cycle...