you have to explain better than that you can see the problem we can't.
>The hot water is venting up the cold water feed from the cylinder 
there is not a cold water feed from the cylinder,      there is a cold feed to the cylinder.  there is hot water feed from cylinder
also how have you connected the cold to the pump and from where ?
how is the hot taken from the cylinder ?
we can't guess.
                
 sonray heating
                
 July 2007