primary / secondary heat exchanger?

[jonwish]

Hi,
Could anyone out there please explain the purpose of the primary and secondary heat exchanger on a combi boiler.
I dont understand why two would be needed.

Apologies for my ignorance.

Mine is an ariston eurocombi a23 mffi

Thanks
Jon

 

[45yearsagasman]

The heated (tap) water must never come into direct contact with the CH water. This is achieved by a secondary (plate ) heat exchanger or a second set of pipes incorporated in the main heat exchanger, sometimes called a dual pass among other names.
Even an ordinary system with a cylinder has a coil inside to prevent cross contamination.