I don’t want to jump on the bandwagon, but please turn off the boiler and call a Gas Safe engineer.
The vast majority of fatalities from gas are not the dramatic bang that destroys a house, it is from carbon monoxide and the easiest way to get a room sealed boiler to produce CO is with an incomplete case seal.
The old Apollo seals did not last all that well so the chances are it is a bit dodgy anyway.
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