To seperater vent pipes in the one cold water cistern in the loft.

[Inverness]

Went to a old farm house today there heating and hot water is open vented. I had a look inside there loft and I noticed the feed and expansion cistern was redundant and beside it is a larger cold water cistern with two vent pipes going into it.
Wouldn't the central heating water contaminated the hot water? Inless it is a prematic cylinder?
Can someone give me advise to why this has happened?

 

[gassafe]

One vent could be redundant...

If the heating is now sealed then it won't have a vent