So British Gas can't fix one of the most common boilers
you'll find. When all they have to do is replace a gas valve.
It's laughable.
Give BG the push.
I would have been around there new O rings or a bit of
gasket paste. Job done and away.
Its not how the Manufacturer states it should be done. So BG don't.
And how do you propose to test the gas valve outlet?