It seems pretty pointless as the only room it vents is the cupboard under my stairs which normally wouldn’t be an issue as that’s not where I keep my son. The prob is that the kitchen cupboards are set into the understairs cupboard and when it’s cold it makes the cupboard cold to the point where the stuff in there gets thick with condensation.

The point of this is what’s the best way to block the damned vent up?

If you are already getting condensation then maybe the vent is needed

It seems pretty pointless as the only room it vents is the cupboard under my stairs which normally wouldn’t be an issue as that’s not where I keep my son. The prob is that the kitchen cupboards are set into the understairs cupboard and when it’s cold it makes the cupboard cold to the point where the stuff in there gets thick with condensation.

Likely where the boiler lived in a previous house design.

Interesting, but I still need to know how to block the vent.

Expanding foam will block it up.

Bogies and peanut butter.

Sounds like you need to vent your kitchen cupboard.

If you have getting condensation you still have a damp but warm cupboard if you won’t you?

Mmmmmm mould.

Mmmmmm mould

Or if you look at it another way, Mmmmmm Quorn

I think I’d rather have the mould!