Please help identify this box on my outside wall?

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Hi folks,

My internal front facing wall shows damp patches and causes the paint to peel off. I asked a plasterer to replace the plaster but he mentioned that unless we fix the root cause the damp would come back anyways. The cause, as per him, is basically a gray box at the same location on the outside (as shown in the photos). The problem is, the plasterer has no idea what this box is and has asked me to figure it out or get it removed before he can come in and re-plaster the section of this wall.

Can someone please help me identify what this thing is? Would covering this box with a plastic sheet or cling film, so that it doesn't get wet during the rains fix the problem or would I have to take it off? Any help really appreciated!
 

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Thanks for the suggestions though the radon vent one does seem scary! I do see few houses around with a box on their outside wall but most of them are fully covered with a metallic box so I'm not sure whether they look similar inside.

I took off the mesh and took a couple of photos but can't seem to easily remove the outer shell.
 

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The plastic grommets here:

Screenshot_20230502-180837_Chrome.jpg


look to me as if (at some point) there has been an electrical connection to the box...
 
Which is the vent for a fan flued gas fire.
Thanks, I do has a gas fire-place in the living room so quite possible it might be a vent for that though I'm not sure why this would be needed given that I also have a chimney!

The big question is -- what would be the best way to handle the damp coming in from this box. Would I have to get someone to cover it with a metallic box which doesn't allow in water or can I simply cover it with plastic? Other DIY suggestions welcome!
 
If your fire is not connected to the box, then it's likely redundant. But get a registered gas engineer to confirm first.

Your condensation issue could relate to a cold bridge from the pipe duct, or cold air in the old duct.

Remove the flue and box and make good, or insulate the void if it's all redundant now.
 
Light the gas fire and see if hot gasses are coming out of the vent?

If the flue is used by a gas appliance I expect that only a Gas Safe engineer is allowed to make changes to it.
 

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