The valley iron is the metal water channel that flows water to your guttering. Some older roofs have ‘bedded in’ valley irons. This is no longer the way roof tilers install irons, as putting sand and cement on metal causes rust!
If the old iron is bedded in, we remove the old mortar, as we do with the ridge caps, replace the valley iron itself and install what’s called “storm seal” (which is like foam soaked in tar). The tiles are then re-laid over the top of the storm seal leaving the valley ‘open cut’ and completely water tight.