I have a american standard 2 handle tub/shower faucet that is not sending water to either the downspout or the shower head, I have great water pressure on both hot and cold cartridges and if I remove the hot side cartridge and turn on the cold side I can get water flow out of the side that has the hot side removed and I have tried this the other way with the cold side removed with the same response. But with both installed and turned on I get nothing at the down spout or shower head, it is however pressurizing the carteridges because after turning off the maintenance shut off valve and removing either carteridge it will blow off in your hand. Any ideas ?