Just bought 3 years old 5bedroom house. Master bathroom has 2 sinks, shower and bathtub. However, bathtub will get only lookwarm out of the faucet even with only hot water on (has separate cold and hot water knobs) while shower and sinks are scalding hot. I assume the same hot water line serves both the shower and bath which are adjacent. And I believe the hot water heaters work together so both provide hot water to whole house. Can't figure out why this would be happening. Any ideas?