When the Furnace Won't Start at All

Most no-heat calls sort into a short list before a panel is even opened: the inducer motor isn't pulling enough vacuum to satisfy the pressure switch, the igniter isn't glowing, the flame sensor lit the burners and then dropped them a few seconds later, or a safety switch tripped somewhere upstream and won't let the sequence start at all. Furnaces are built to fail safe — when something is wrong, the control board stops the sequence rather than pushing gas into a burner it can't confirm is burning cleanly.

That fail-safe behavior is also why 'it just needs to be reset' is rarely the whole answer. A furnace that locks out repeatedly is telling you the same fault keeps happening; cycling the breaker gets you one more attempt, not a fix. Whoever comes out should be checking why the lockout is happening, not just clearing it and leaving.

What this usually involves

• Ignition failures — igniter or spark won't light the burners
• Furnace lights, then shuts off a few seconds later
• Repeated lockouts on the control board
• Blower runs but no heat, or no blower at all
• Inducer motor or pressure switch faults

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