We are having a first floor addition built with a bathroom and radiant heat in one room. The plumbers roughed in the supply lines, which have shutoffs installed. The shutoffs are obviously in the off position. This "supply line branch" also serves an existing first floor half bath. Since the rough in was done, we have experienced a change in the hot water supply to an upstairs shower, which is on another "supply branch" that runs away from the hot water heater in the opposite direction than the branch to the addition. With the faucet set right at halfway between hot and cold, the water temperature was perfect for showering. Since the rough in, the faucet has to be set all the way to hot for the temperature to become warm enough to shower. The plumbers claim that it is impossible for their rough in to have caused this change. Their way of "fixing" the problem was to set the hot water heater at it's hottest setting. This allows the shower upstairs to be warm enough when it is set at halfway again, but makes the hot water throughout the house extremely hot when just the hot water is turned on. With young children in the house, we are afraid of the risk of accidental scalding. We are also uncomfortable with the hot water heater set at the hottest setting. Does anyone have a clue as to what steps if any can be taken to allow the addition to have hot water without changing the availability of hot water in the existing lines in the rest of the house?