heating system

Hi all, Just wondering if someone can help me identify this water tank / container, and let me know how I should be maintaining it. It sits alongside my main water tank, and, as can be seen from the attached images, it's quite dirty. The overflow pipe leads out the back of the house, but...

Hi guys I know this is for the old heating system I've now got a combi boiler but what is it called amd what was or is its function?

Soo I’m looking at changing the solenoid on my three way valve (hence it’s not on in the picture) but looking at the system I cannot work out what the branch offtake between the pump and the three way valve is? Take a look at the pic