Gas Fitter Practice Test

Which component is identified as open when the thermostat terminals read 0V with the gas valve coil terminals also reading 0V?

1. Gas valve coil

2. Thermostat

3. High limit

4. Transformer

The correct answer is: Thermostat

When the thermostat terminals read 0V and the gas valve coil terminals also read 0V, this indicates that there is no power being supplied to either component. In this scenario, the thermostat is identified as the component that is open, meaning it is not allowing electrical current to flow through to the gas valve coil. In typical systems, the thermostat is responsible for controlling the operation of the heating system by completing the circuit when there is a demand for heat. If the thermostat contacts are open, it prevents voltage from being transmitted to the gas valve coil, which governs the gas flow to the burner. Consequently, if both terminals are at 0V, this strongly suggests that the thermostat is not functioning correctly or is in an open state due to a lack of thermal demand or a malfunction. Understanding this concept is crucial for troubleshooters, as diagnosing the root cause of a heating issue often begins with examining the thermostat's operation and verifying its state. In contrast, the high limit switch, transformer, and gas valve coil are likely functioning normally since their readings reflect no power is reaching them, which is dependent upon the thermostat's closed (active) state.