Furnace Inducer Motor

First to start, and for good reason

When the thermostat calls for heat, the inducer — sometimes called the draft inducer or combustion blower — spins up first. It creates negative pressure in the combustion chamber and pushes exhaust gases through the heat exchanger and out the vent. Only when the pressure switch senses that this draft has been established does the control board move on to ignition.

This is the mechanism that replaced the natural-draft chimney on older furnaces. It makes sealed-combustion and high-efficiency venting possible, and it makes every cycle verifiably safe before gas flows.

Symptoms of inducer trouble

• A loud whine, rattle or vibration from the top of the furnace at the start of a cycle
• The inducer runs but the furnace never advances to ignition — often a pressure switch or blockage issue
• The inducer does not run at all and the furnace sits silent
• Repeated lockouts with a draft or pressure-related fault code
• Intermittent operation, more common on cold mornings

Why inducers fail

• Bearing wear after years of continuous cycling
• Condensate corrosion in the housing, particularly on high-efficiency furnaces
• Debris or nesting material in the vent restricting flow
• Cracked or disconnected pressure tubing giving false readings
• Electrical failure of the motor windings or a bad relay on the control board

Inducer or pressure switch?

These two parts are diagnosed together because their symptoms overlap. A pressure switch that will not close might be faulty — or it might be correctly reporting that the inducer is not producing enough draft, or that the vent is partially blocked. Replacing a pressure switch to silence a fault caused by a blocked flue removes a safety check while leaving a genuine venting hazard in place.

Proper diagnosis measures actual draft pressure and compares it to the switch's rating rather than guessing.

A Northern Colorado note

Sidewall-vented high-efficiency furnaces are common in newer Fort Collins and Timnath subdivisions. Heavy snow, drifting and ice can partially block those terminations, which shows up as intermittent draft faults during storms. Keeping the intake and exhaust clear is on our winter furnace checklist for exactly that reason.