Hi! Thanks for that! I tried the silicon seal that is around the lid, but it didn't fit very well and created too much friction - a nightmare, as you said. I'm waiting on one or two bits of kit to be delivered and I'm ready for my first recirculating mash. I read a post rubbishing the sensors sourced from China, saying they weren't accurate. How have you found yours? I've ordered one from Angel Homebrew, but it's 80cm long, so some adaptation to the tee piece was needed. Now I'm worried that the sensor might impede the flow of the wort - there's always summat t'worry about! I'm going to place mine in the "elbow" of the tee so that there's no "corner" for the wort to turn. Do you think this might be the cause of your airlock problem?