Central Heating Boiler Exhaust Pipe fitting

Noticed this at one end of where the white pipe leads from boiler to vent outside, I'm concerned as I can actually see the silver wall insulation, there's a similar gap but not as big on the left side.

Is it important that the gaps are sealed on the plasterboard? If so will normal filler be enough as I'm pretty sure it could fall down inside the wall.

Image attached of pipe above the kitchen gas boiler.

 

Perhaps it's left with a gap for safety reasons.

 

seal it with sand and cement

 

????

 

Yes it's an air gap to prevent the sand and cement catching fire !!

 

should it be fully sealed?

 

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