Overflow constantly dripping

[Donny]

Hello

I have a tank in my loft I think it's called a header tank (sorry for the non technical descriptions) it has a big tank on the bottom and a small one on the top with a ball cock in it. To get hot water out of the taps I have to flip a switch which I can hear turns on the immersion? in the loft. The only problem is every time I flip the switch the over flow pipe starts running.
I was advised to bend the ball cock which I've done but it's still running.
Im guessing the tank filling to quickly?

 

[kay-jay]

Your hot water is overheating. Call a professional. It's not something you should be playing with

 

[Dotty]

Job 38.11