Air leak on a boiler flue

Our gas boiler has been serviced today, with the windy weather I have noticed a draught around the flue. Is that something that should be airtight?
I have found a product that acts like a grommet, I would get my gas engineer to fit it.

The FlueSnug is for new installs and needs an oversized hole to insert the snug before adding the flue. It has limited potential in your case unless you want a major (read “expensive” job)

I thought of this:

But it still needs the flue to be removed and reinserted, admittedly without re-drilling the wall.

I think your best bet is to build up an airtight barrier of short strips of airtightness tape arranged around the flue. Alternatively use a brush on liquid airtightness membrane. Those that are familiar with my posts know already which one I suggest!

If the flue penetration is on view you can buy the white version.

It doesn’t matter how it looks on the inside. Is it important to have a seal on the outside?

If you have cavity walls it is essential to seal both sides, to stop uncontrolled ventilation of the cavity. Otherwise I suggest it anyway to stop damp ingress.