Warm water out of cold tap

19Gra40

I have an alde boiler in new lunar stellar . With boiler on ,when I draw cold water, it runs cold then after seconds runs warm  then cold then warm again, this still happens  after running a few minutes. It is not caused by pipes touching hot pipes as  
I didnt have  the   heating on  , and I hadnt drawn any hot water. The pipe from the aqua roll I notice tees off to the bottom of the boiler on route to cold tap, which to me points to drawing warm water from the base of boiler, on route to cold tap. Does
anyone know if the said tee piece is also a non return valve .