I recently had a plumber installed a new FHW boiler and an indirect HTP SuperStor 45 gallon WH. The hot water in the main bath needs to be turned much higher than with the previous 25 yr old DHWH and only lasts about 15 minutes. I called my plumber and he said its possible that by turning off the water to do the job, debris might have loosened, causing this issue. I haven't noticed the issue with any other faucet in the house because I don't leave any other source on for that length of time. I am wondering, a) what is the likelihood of the shower faucet being the problem (its a single star-shaped head), b) is there a mixing valve, or something similar I can add to make the hot water last longer, c) is there anything else that may be a culprit, d) is there anything I can do myself to make the hot water last longer, short of telling my pregnant wife to take shorter showers (that didn't work)?