Baxi 105 flue- additional air test point?

[bewsh]

I've come across a few baxi 105e flues, where they go from 4" to 5", they have what looks like an additional air intake test point, but the cap is always missing? Baxi are a nightmare and never know what I'm on about and don't give me the correct part number for the cap. I've just put a female iron on it with some gas seal.

does anyone know what this test point is for and why the cap is always missing? Also if you have the part number for the cap, that would be greatly appreciated. There's a pic just in case you don't know what I'm on about, it's a bit dark though sorry lads

http://s14.postimg.org/61sjsif1t/Full_Size_Render.jpg

 

[bewsh]

Just realised this is in open forum, please move

 

[buckley plumb]

Seen them myself normally on potterton straight onto of boiler to vert flue. I don't know why as when I fit duotec which is same boiler vert flue fits straight in.

 

[Dotty]

Moved

 

[GrahamM]

You sure it is not blanked off inside?
Think it is a condensate collector port for long extended flues.

 

[bewsh]

I couldn't quite see that one as it was in a really small cupboard and it was in line with the plaster board ceiling. But possibly blanked off. Just checked a cap on it just to be safe