Furnace Noise Guide: What Your Furnace Is Telling You in London, ON

A loud banging noise (often called furnace kettling or detonation) usually indicates delayed ignition. Gas builds up in the combustion chamber before igniting, causing a small explosion. This is dangerous and can damage your heat exchanger, leading to carbon monoxide leaks. Turn off your furnace immediately and call a TSSA-certified technician for emergency service.

Squealing or screeching typically points to blower motor issues — worn bearings, a loose belt, or motor failure. This reduces airflow and heating efficiency. If ignored, the motor can seize completely, requiring full replacement. Turn off the furnace and call for repair to avoid a complete breakdown during cold weather.

Rapid clicking usually means the ignitor is trying to light the gas but failing. Common causes include a dirty flame sensor, faulty ignitor, or gas supply issues. The furnace will try 3-4 times before locking out. Turn the furnace off at the thermostat, wait 5 minutes, then try resetting. If clicking continues, call a technician.

Rattling often comes from loose panels, screws, or ductwork. Check if the furnace cabinet door is secure. If that doesn't stop the noise, the inducer motor or blower wheel may have loose components. Loose ductwork can also rattle when the furnace runs. A technician can tighten components and secure ducts during a service call.

A low hum is often normal (transformer or inducer motor). However, a loud or new humming sound can indicate electrical issues — a failing blower motor capacitor, stuck contactor relay, or transformer problems. If accompanied by burning smells or the furnace not starting, turn it off and call for service immediately.

Yes. A severely clogged filter restricts airflow, causing the blower motor to work harder, which can create humming, rattling, or whistling noises. The motor may overheat and shut down. Change your filter every 1-3 months. If noises persist after changing the filter, call a technician to check the blower motor.

A cracked heat exchanger may cause a rattling or metallic ticking sound as metal expands and contracts. More seriously, it can cause a whooshing sound or allow carbon monoxide into your home. If you hear these sounds along with CO detector alerts, musty odors, or flu-like symptoms, evacuate immediately and call 911, then a technician.

Our diagnostic fee is $175, which includes a complete inspection of your furnace, noise identification, and repair recommendations. The diagnostic fee is waived if you proceed with the repair. We provide upfront pricing before any work begins — no surprises. Unlike companies that charge after-hours premiums, our 24/7 emergency service has zero surcharge.

Replace your furnace if it's over 15 years old and requires major repairs (blown motor, cracked heat exchanger, failed gas valve) costing $800+; if it needs frequent repairs; or if the heat exchanger is cracked. A new 96% AFUE furnace starts at $3,400 installed. After $650 Enbridge rebate, net cost is $2,750 — often worth it compared to repairing an old, inefficient unit.

Prevent furnace noises with annual professional maintenance ($149/year for Basic Plan). During tune-ups, we clean burners, lubricate moving parts, tighten electrical connections, inspect the heat exchanger, and check the blower motor. Regular filter changes (every 1-3 months) also prevent airflow-related noises. Most noise issues are preventable with proper maintenance.