Airlock?

[Legion]

Assuming the you are gas registered, as you should be to work on boilers, then you should be asking these questions in the Combustion Chamber on this site which is reserved for trade discussions

You seem to have virtually no idear of what you are doing. Its frankly embarasing to me that the public can see someone with virtually no knowledge at all, apparently working on customers systems. With so little experience that could be dangerous or cause damage, I strongly suggest you make all your future postings there!

I strongly suggest you take a course in Engleesh Grammer you are embarrassing. Illiterate mouthpiece , you shame yourself with your ignorant pretensions. your ill education shines through,