In a different no heat call scenario, if the high limit terminals read 110 volts while the thermostat terminals read 0 volts, which component is identified as open?

In this scenario, the reading of 0 volts at the thermostat terminals indicates that there is no voltage present to signal a call for heat. This situation typically suggests that the thermostat is either not functioning or is set to a temperature below the ambient temperature, meaning it isn't calling for heat.

On the other hand, the high limit switch reading 110 volts means that it is closed and allowing current to flow, indicating that it is functioning correctly and not open. The purpose of the high limit switch is to prevent overheating by interrupting the current if temperatures exceed safe operating limits; in this case, it is not the source of the problem.

Therefore, given that the high limit switch is operating normally while the thermostat terminals show no voltage, the correct conclusion is that the thermostat must be open or defective, as it is not providing the necessary signal to initiate heating. This aligns with the readings presented in the question.