Many brewers wrongly assume that the yeast is not working because there is no bubbling through the airlock. The airlock is fitted to allow gas to escape and prevent micro-organisms and wild yeasts from entering the fermenter. Do not rely on the airlock as an indicator of fermentation activity. Rather than becoming “mesmerised” with the airlock, look for condensation inside the lid, a scum ring at the top of the wort, sediment on the bottom, cloudy / turbid / foamy brew from the tap and the specific gravity dropping (use a hydrometer).