A customer reports that their direct hot surface ignition furnace will not light despite the inducer motor running. What is likely the fault if 17 VAC is measured at the gas valve?

In a direct hot surface ignition furnace, the gas valve requires a specific voltage to open and allow gas to flow for combustion. If 17 VAC is measured at the gas valve, this indicates that there is some level of signal being sent to the valve but not the full 24 VAC typically needed to fully activate it.

The most plausible explanation for this situation is a fault in the electronic control board. The electronic board is responsible for coordinating the operations of various components, including signaling the gas valve when to open. If the electronic board is malfunctioning, it may not be sending the proper voltage to the gas valve, leading to an insufficient voltage reading. This scenario aligns with the symptoms described: the inducer motor runs, indicating that the system is powered and attempting to operate, yet the gas valve does not open as it should due to the incorrect voltage level.

In contrast, other issues such as igniter malfunction, pressure switch failure, or flame sensor problems would likely prevent the system from reaching this state where the gas valve receives an inadequate voltage; these components interact at different points in the ignition sequence and would generally have more definitive indications if they were at fault. Thus, a failure within the electronic control board is the most likely cause of the situation