Trying to figure out how to diagnose the master shower in a 26 year old house. It takes an extreme amount of time to get hot water. The other shower (in next room) and all of the sinks all get hot water quickly. I finally bought a temperature sensor led shower head so I could tell when to bother to get undressed, but it is wasting five minutes of water while I wait. Could it be the control (MIXET) causing this ? Or?