After noticing a drop in pressure on the boiler I later found (after noticing a wet ceiling) a leak coming from the techno-varia auto air vent 1/2 on our central heating manifold (please see attached photos). The grey automatic vent (rather than black manual vent) was the source. I have since screwed the automatic part shut to stop the leak in the meantime. Could this have worked loose, or should I replace the whole unit to be sure? I have found it for sale for not much more than £5 but wondered what peoples thoughts were? Thank you.