What is often used to measure the temperature inside a boiler?

The correct choice for measuring the temperature inside a boiler is a thermometer. Thermometers are specifically designed to provide accurate readings of temperature, which is crucial in the safe and efficient operation of a boiler. Maintaining the proper temperature is essential to ensure that the boiler operates within safe limits and efficiently produces steam or heated water.

Flow meters measure the quantity of fluid passing through a system, but they do not provide temperature readings. Pressure gauges indicate the pressure within the boiler system, which is important for safety and performance, but again do not measure temperature. Water flow sensors are used to detect the flow rate of water but are not capable of measuring temperature directly. This distinction underscores why a thermometer, designed for that precise purpose, is the appropriate instrument for monitoring temperature within a boiler.