Expansion Vessel - Not sure abouts its purpose

[Rob Foster]

Can somebody please explain the function of the expansion vessel on my heating. Is it to absorb the increased volume of water when its hot or/and to be a reservoir of water to top up the heating system when there are small drips Many thanks

 

[rpm]

What is a heating expansion vessel? - Google Search

 

[ShaunCorbs]

For expansion and contraction eg when your heating system is hot the water expands