In a direct spark ignition system, the igniter is sparking, but the main burners will not light. Which of the following is an INCORRECT test to perform?

In a direct spark ignition system, ensuring that the thermostat is closed by checking between the terminals is typically a valid test to confirm that the system is signaling that it’s ready to ignite. When the thermostat is calling for heat, it should complete the circuit, allowing for proper operation.

However, performing the test from terminals “W” to “C” is not directly related to identifying issues with why the main burners are not lighting when the igniter is sparking. This test is more about confirming the signal from the thermostat to the heating system rather than addressing fuel flow or blockage at the burner level, which are more relevant factors in this scenario.

In contrast, testing for continuity in the igniter wire, ensuring the gas supply is turned on, and inspecting the burner assembly for blockages are all critical diagnostic actions. Each of these tests directly relates to fuel delivery or the igniter’s effectiveness in igniting the gas at the burner steps, offering a better insight into why the burners may not be lighting despite an igniter spark.

Thus, understanding that the test of checking terminals "W" to "C" may not assess the immediate ignition problem enables one to focus on more pertinent checks that can directly affect burner operation.