To be fair, at a guess, the original installer may have been at fault for leaving a redundant pressure guage on there, I don't know for sure though, could have been left in case you wanted it as a sealed system in the future.
Fair enough, but you guys managed to point me in the right direction without even seeing the boiler. Seems the lack of pipe and the additional pipe leading to the loft were a bit of a clue.
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