Which Pressure Gauge Determines Saturation Temperature in a Closed Loop Pipe?

[Sheroff]

water is flowing in the closed looped pipe equipped with preheater. there are pressure and temperature gauges before the preheater and after the preheater. which pressure gauge should i use to know whether the outlet preheater temperature has reached the saturation temperature?

 

[BvU]

Hello Sheroff,

The one on the outlet side.