Match the noise
| Noise | Where it usually comes from |
|---|---|
| A boom or bang as the burners light | Delayed ignition: gas building up for a moment before it lights |
| A squeal or screech | A blower motor bearing, or a belt on older belt-drive furnaces |
| A rattle or vibration | A loose panel, a loose part in the blower, or a failing draft fan |
| A scraping or grinding | A blower wheel touching its housing, or a failing bearing |
| A hum or buzz with no start | A motor trying to start and failing, often a capacitor |
| Ticking or popping as it heats and cools | Ducts expanding and contracting, usually harmless |
The one to act on
A boom when the burners light is not a noise to live with. It means gas is gathering for a moment before it ignites, which can come from dirty burners, a weak igniter, low gas pressure or a combustion problem. Each small bang stresses the heat exchanger. Turn the furnace off at the thermostat and call.
If any noise comes with a smell of burning plastic, scorching, or a carbon monoxide alarm, leave the house and call from outside.
The ones that warn you
A squeal or a grind from the blower usually means a bearing on its way out. It will often keep working for a while, then stop on a cold night. A rattle from the draft fan, the small motor that pushes the exhaust out, is worth attention for the same reason: when it fails, the pressure switch will not close and the furnace will not light.
The ones that are usually harmless
Ticking and popping from the ductwork as it warms and cools is metal moving. A whoosh as the burners light is normal; a bang is not.
What to tell us when you call
What the noise sounds like in your own words, when it happens (at start-up, while running, at shut-off), whether it is new or getting worse, and whether the furnace still heats. A short phone recording of the noise is useful if you can make one from a safe distance.
No heat? Tell us what the furnace is doing.
Gas, electric and high-efficiency furnaces across Caldwell, Nampa, Middleton and Parma. Start with the symptom and your ZIP code.
You'll be asked for your ZIP code first, so your call reaches a technician who covers your area.