Airlock not bubbling

[bilgerat]

My first post here for a while Im just getting back into brewing after a hiatus of a year or so.

I have a choc/oatmeal stout in a new fermenter and the airlock isnt bubbling, however there is a nice bubbly looking crust at the top of the brew, I recently made another brew in this new fermenter and had the same problem, there was no bubbling from the airlock however that brew turned out reasonably well, my other fermenter has a brew in it that is bubbling away nicely ?

I have swapped lids on these fermenters to see if the rubber seal the cause of the problem and I have put a heater under the fermenter that isn't bubbling, but nothing has changed, the yeast I used in the stout brew is Wyeast 1084 Ale yeast

The SG has dropped from 1050 to 1033 in two days I just don't understand why it isn't bubbling?

Any suggestions appreciated
Bilgerat.

[barls]

don't worry about the airlock. its dropped in gravity so id be happy. look for the other signs of fermentation.
the krausen and change in clarity and most importantly the gravity to drop

[lethaldog]

If there's action I wouldn't be concerned, obviously just a dodgy seal!

[bilgerat]

OK thanks for the replies.