a boiler has how many condensing pipes?

[bluesky]

Hi guys,

I am doing some gas training now. A couple of days ago I helped a gas fitter installing a vaillant combi boiler. I think there are 2 condensing pipes. He connected one to the drain and the other one to outside directly. We were busy and I did not have time to ask him. So why boiler has 2 condensing pipes, or only vaillant boilers do?

thanks a lot.

 

[Billy Bob Bob]

they all only have one,the other one would be the prv

 

[bluesky]

thanks gasman,