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Furnace Blower Runs but Won’t Ignite: Safety Switch Repair in Las Vegas

When the furnace blower runs but the burners won’t ignite, the furnace is often stopping itself on purpose. Before it lights, the control board checks a chain of safety switches (such as the pressure switch, high-limit switch, and rollout switch), and if one of them reads open, the board won’t start ignition. Many boards also run the blower nonstop when the limit is open. On December 10, 2025, a Las Vegas home in the 89130 ZIP had this exact symptom: the blower ran, but the burners never lit. We replaced the furnace’s safety switches, and the burners lit again.

Furnace Blower Runs but Won't Ignite: Safety Switch Repair in Las Vegas

What We Found

The homeowner told us the blower on the furnace was working, but the igniter wouldn’t light the burners. The furnace is a Ruud Silhouette upflow model in the garage. Testing pointed to the furnace’s safety switches. While the furnace was open, we also looked inside the heat exchanger with a borescope camera and found rust on the indoor coil.

How We Fixed It

  • Replaced the furnace’s safety switches.
  • Fired the furnace and watched the igniter light all three burners.
  • Checked draft pressure with a manometer, which read about 0.8 inches of water column.
  • Inspected the heat exchanger with a borescope camera.
Furnace Blower Runs but Won't Ignite: Safety Switch Repair in Las Vegas
Furnace Blower Runs but Won't Ignite: Safety Switch Repair in Las Vegas, job photo 2
Furnace Blower Runs but Won't Ignite: Safety Switch Repair in Las Vegas, job photo 3
Furnace Blower Runs but Won't Ignite: Safety Switch Repair in Las Vegas, job photo 4
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How it turned out

The burners lit with steady blue flames after the switches were replaced. The homeowner also received options for a blower wheel replacement and for a full system replacement down the road.

Is it the igniter or a safety switch?

Watch the startup. With a bad igniter, the inducer motor runs and the igniter never glows, or glows and nothing lights. With an open safety switch, the furnace usually never reaches the igniter step, and the blower may keep running. Our hot surface igniter replacement covers the igniter side, and our pressure switch diagnostic covers a furnace that starts and then shuts off.

Why do furnace safety switches fail?

They trip when something is wrong: a dirty filter or blower that lets the furnace overheat, a blocked vent, or a weak inducer motor. They also wear out with age, and a switch can fail open even when nothing else is wrong. A technician tests each switch and the condition behind it, so the new switch doesn’t trip again for the same reason.

Can I reset or bypass a safety switch myself?

Some rollout switches have a reset button, but if one tripped, the furnace had a reason. Don’t jump or bypass a safety switch to get heat. These switches keep flames and exhaust where they belong. Turn the furnace off and call for service.

Safety note: HVAC repairs involve high voltage, refrigerant and, on gas furnaces, combustion gases. Leave them to a licensed technician.

Team of Bob's Repair technicians in Paradise, NV, performing maintenance on outdoor AC units to extend their lifespan, set against the backdrop of a local home and a palm tree.

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