Hello all. We're having problems with the flow in our main upstairs bathroom, I've measured it at under 2.5 gpm at both the faucet and shower spout with the head removed. We're plumbed with copper to the fixture (an older Delta model, maybe 80s by the look of it) and, while I haven't checked the house pressure (how would one do that, exactly?), we are seeing significantly higher flow rates at other faucets on the same level of the house. Am I right in thinking this likely suggests a blockage or buildup in the tub/shower valve, or could there be another culprit? And what would be my best option to try and take care of a bad valve? Happily, it's is easily reachable through an access panel if it has to be replaced. Thanks.