My Expansion tank does not have a ball cock?

[mjdalby]

Hi

I can not find how to stop my heating system refilling. I have located the expansion tank and it does not have a ball valve. It is located within the hot water system domestic hot water feed tank (which has a ball valve)

Basically i drained about 5 litres out of my system so that i could add a cleaner in. I have added the cleaner to the expansion tank but it is just sitting there (even when i bleed the radiators) as it must be already full.

The expansion tank has a large rod of metal in the bottom which I am thinking might be some sort of alternative valve that connects to the system and i need to some how shut this before i drain the system?

if anyone could shed some light on the situation i would much appreciate it

thanks