I have a tub/shower combo with 1 round handle - pull the handle out, then turn to adjust hot/cold. For the shower, you pull up the little knob on the tub faucet. Same in 2nd bathroom that is also upstairs. Until 2 months ago, had loads of hot in tub; now have to run the handle on full hot and barely get 1/4 full of not so hot. But the shower has no problem. Any help?