Where is the test gauge typically connected?

The test gauge is typically connected to the boiler because this allows for the direct measurement of the internal pressure of the system. This connection is essential for determining whether the boiler is operating within the safe pressure limits as defined by regulatory standards. Monitoring the pressure at this point helps ensure that the boiler is functioning properly and safely.

Connecting the test gauge to the boiler provides the most accurate representation of the system's operating conditions. It allows operators to make informed decisions about maintenance, safety, and the overall efficiency of the boiler.

In contrast, while the other locations mentioned could have their uses, they do not provide a direct reading of the boiler pressure. For example, connecting a gauge to the hydronic pump or expansion tank may yield readings influenced by other system components and not the boiler's actual pressure. Connecting it at the safety valve also does not reflect the pressure throughout the boiler, but rather only the pressure at that specific safety point which is intended to release excess pressure. Hence, the boiler is the most logical choice for accurate pressure assessment in the context of a high-pressure boiler system.