I need to tap in to the central heating due to an extension with underfloor heating that’s gone in. I want to be more than sure before tapping into the system due to its complexity and being an open vent I’m going to freeze the pipes I need to, so I can work on them. I was hoping to double check on here to avoid making a mistake. The two 28’s I believe are the flow and returns for the cylinder and the two 22’s on the left are for the Heating. I noticed there’s a tee branching off and running alongside the heating pipes. Is that a bypass or the actual vent for the heating? Never worked on these systems before so sorry if I come across as clueless. I think I’ve attached a photo of the boiler. Thanks!