You are wrong. The seal on an Intergas case does not seal the products of combustion only air. Will you please give us some legal reference to your assertions?Not a DIY job I'm afraid - in common with most other makes of boiler, the case forms the safety room seal and as such should only be removed and replaced by a Gas Safe Engineer capable of carrying out the regulatory 26.9 checks on completion. DIYers should not be removing it to do anything at all.