We have air vent in kitchen pantry letting in a massive amount of cold. There is a boiler in the pantry of a sealed room variety. It clearly says in the manual that no additional ventilation is required other than the flue which draws in air and expells waste products. We have no gas cooker. There is a gas fire in the living room. We also have trickle air vent around the house which can be open and closed rather than permanently open. Can the ventilation bricks in the pantry be safely blocked up? Thanks.