Mike PleziaInside service technician, Clark Associates · Commercial Equipment, HVAC, and Refrigeration professional

The Gas Valve Is the Last Thing to Check

14 Oct 2026 · 1 min

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0:56

In this concise instructional video, the speaker addresses new HVAC technicians and explains the proper diagnostic order for a furnace that is not producing heat. He emphasizes that the gas valve should be examined only after confirming that earlier steps in the furnace start‑up sequence have succeeded: the inducer motor must have established proper draft, the pressure switch must be closed, the igniter must reach its operating temperature, and the control board must have sent a 24 V signal to the valve. The speaker provides a quick checklist—verify igniter glow, pressure‑switch status, and 24 V at the valve terminals—before concluding that a non‑opening valve is the likely fault. The overall message is to follow the sequence methodically, using the gas valve as a last‑resort suspect, and to share this knowledge with others.

Chapters

Hey, are you new to the trades? Here's something you may not know about gas valves and how they fit into the furnace sequence. The gas valve is not the first thing to check on a no heat call; it's near the end of the sequence. By the time the gas valve should open, the inducer has already proven draft, the pressure switch has closed, the igniter has reached temperature, and the control board has given the go-ahead. If the gas valve isn't opening, ask what came before it. Is the igniter glowing? Is the pressure switch closed? Is there 24 volts to the gas valve terminals? If you have voltage to the valve and it's not opening, then the valve may be the problem. But only then! The sequence is your guide. Follow it in order, and the gas valve will be the last thing you suspect, not the first. Now that you know, you can help someone else know.