Crossover is a term that is used when the hot water “crosses over” to the cold or the cold water “crosses over” to the hot. The frequency of customers calling in with these symptoms is increasing. Having some hot water mixed with your cold is not necessarily an urgent situation, but it does indicate that there is a problem and it is certainly not energy efficient. Having cold water crossing over into your hot water lines often results in a lukewarm shower and that usually gets everyone’s attention! It can also result in reduced water temperature at the dishwasher which can lead to an unsanitary condition as well as additional water spotting.
Pinpointing the cause of crossover can be very difficult and time consuming. Obviously, if the water system is plumbed incorrectly you can get crossover symptoms, but if your system has been working satisfactorily and then starts exhibiting crossover symptoms the problem is somewhere else. Single handle fixtures, washing machines, and oversized circulation pumps are some of the culprits that can be the source of crossover. Since 1994 safety shower valves (pressure balanced or thermostatic) have been mandated. Often components of these valves can stick and cause crossover. Check valves on circulation systems can malfunction allowing water to flow the wrong direction. Water heater dip tubes can wear out, allowing under-heated or cold water to enter the hot water line.
Whenever presented with these symptoms, and a crossover is suspected, the approach needs to be methodical and thorough. Sometimes there will be more than one source and the issues will need to be addressed one at a time.