I understand that some building jurisdictions require that pressure relief valves be installed on tankless water heaters, but other jurisdictions do not require this. The manual for my Weil-McLain boiler does not call for one. I can understand a pressure relief valve on a vessel such as a boiler, but why put a pressure relief valve on the cold water pipe going to a tankless heater? A tankless heater is just a coiled pipe with fins. What could possibly raise the pressure to the point that the pipe explodes?