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?
