Gas Fitter Practice Test

If the gas valve coil reads 0V during a no heat call, which component may be open?

1. Gas valve coil

2. Thermostat

3. High limit

4. Transformer

The correct answer is: Thermostat

When a gas valve coil reads 0 volts during a no heat call, it suggests that the circuit that normally energizes the valve coil is not completing, preventing the gas valve from opening. This situation often indicates that the thermostat is not signaling a heat demand. The thermostat acts as the control point for the heating system; when the temperature in the space is below the set point, the thermostat closes its contacts, allowing voltage to flow and energizing the gas valve coil. If the thermostat contacts remain open, it won't send the necessary signal to activate the gas valve, resulting in a 0V reading at the gas valve coil. In contrast, the gas valve coil itself should normally be energized when a heat demand exists. Therefore, an open state in the coil wouldn’t explain the 0V condition unless there is a broader issue within the system. Components like the high limit switch or transformer might influence the system's operation, but if these components are functioning correctly, their states wouldn’t directly lead to a 0V reading at the gas valve coil during a no heat call. They may affect the overall control circuit, but the most direct cause of a 0V reading in this case points to an open connection or failure within the thermostat.