A grinding noise that started this week

Why waiting turns one repair into two

Metal on metal removes metal. A dry bearing eats its own shaft, and a wheel rubbing its housing wears both. A motor run to seizure often takes the wheel with it, and sometimes the board it stalled against.

The noise is also a countdown on the heat. A seized inducer stops the furnace running at all, because the control will not light a burner it cannot vent. In Vineland, NJ, with about 108 nights a year below freezing, that turns a scheduled repair into a house with no heat on the night it happens.

What the noise says about which motor

Starts a few seconds before the burner lights, stops shortly after it. That is the inducer, the small motor that clears the flue before ignition.

Starts a minute or so after the burner and keeps running after the flame is out. That is the blower.

A screech on start that settles is bearings. A steady scrape at running speed is more often the wheel touching something. A rattle that changes with blower speed can be a wheel loose on its shaft.

What the visit involves

A technician runs a full cycle and listens at each stage, then shuts it down and turns each wheel by hand — a dry bearing is audible standing still. After that comes endplay on the shaft and current draw under load: a motor pulling above its plate rating is working against its own bearings, and that number decides motor against wheel.

What to say when you call

• Where in the cycle the noise starts, and where it stops
• What it sounds like: grind, screech, rattle, scrape
• Whether it has got louder, and how long it has been there
• Install year, your address and ZIP code

Common questions

Can it wait until spring? The heating season is when it will be asked to run every night, and that is when a worn bearing finishes. Waiting moves the repair to the coldest week rather than avoiding it.

Is the noise itself dangerous? On its own it is a wear report rather than a hazard. What it costs is the choice of when: a motor that seizes picks the hour instead of you.

Can the bearings be oiled? Most blower and inducer motors built in recent decades have sealed bearings with no oil ports at all. When those go, the motor is replaced rather than serviced.