Should New Flue Be Cemented In Gap Between Brickwork?

[woodbine]

We recently had a new Remeha boiler fitted by a Gassafe engineer.

I have noticed that the gap betwwen the flue and the hole in the brickwork, both inside and outside, is only covered by a large rubber flange/groomet that fits tight around the flue.

Should this small gap be cemented outside, as well as cemented/plastered inside? Is the grey rubber grommet sufficient on its own?

 

[transam]

Providing the grommet is sealing , it should be O,k , some of these flue's are or were designed to be fitted in high rise building's , from inside the building , grommet seal , as u would have difficulty making good the outside 6 floor's up (for example )

 

[PEDANTICVINDICTIVEMAN]

I prefer to cement both inside and out then the rubber grommets over the top, if it's high rise then just inside, mainly to hold the flue secure in position and correct angle, if the holes are core drilled then then the rubbers should seal adequetly to stop products of combustion from entering the building, but if you can move flue I wouldn't be happy as they are mostly push fit.