The water in my shower comes out mostly from the tub faucet and not the shower faucet (which I assume is a problem with the diverter) but what I don't understand is that the water pouring out of the tub end is scalding hot, while the water coming out of the shower end is only warm. Then they both shift to cold. Why would there be a difference, and how can I take a hot shower? Please help. It's chilly.