Boiler Making Noise?

Kettling — Rumbling / Boiling Sound

This is the most common boiler noise we hear about in Vancouver. It sounds exactly like a kettle boiling — a deep rumbling or gurgling from inside the boiler.

• Cause: Water can't flow fast enough through the heat exchanger, causing localized boiling and steam bubbles that collapse violently (cavitation).
• Root causes: Sludge buildup restricting flow, failing circulation pump, blocked plate heat exchanger, or incorrect pump speed setting.
• Danger level: Moderate — not an immediate safety risk but will damage your heat exchanger over time. A kettling boiler is running at reduced efficiency.
• Fix: Power flushing to remove sludge, pump replacement if failing, or heat exchanger cleaning. In severe cases, heat exchanger replacement.
• Cost: Power flush $500-$800. Pump replacement $400-$700. Heat exchanger replacement $1,500-$3,000.
• Prevention: Annual professional maintenance with combustion analysis and water quality testing.

Banging / Knocking — Explosive Sound on Startup

A single loud bang when the boiler ignites — like a small explosion — is delayed ignition. Gas builds up in the combustion chamber before the igniter sparks, causing a small explosion when it finally lights.

• Cause: Delayed ignition — gas accumulates before the spark fires. This is a safety concern.
• Root causes: Dirty or worn ignition electrode, incorrect spark gap, failing ignition transformer, gas valve slow to open, or burner ports partially blocked.
• Danger level: HIGH — unburned gas accumulating in the combustion chamber is dangerous. Do not continue using the boiler if this happens repeatedly.
• Fix: Ignition electrode cleaning or replacement, burner cleaning, gas pressure adjustment. Call a licensed gas fitter — this is not DIY.
• Cost: Ignition electrode replacement $200-$400. Burner cleaning $150-$300.

Whistling / High-Pitched Squeal

A whistle or squeal that changes with boiler operation usually indicates air or flow issues.

• Cause: Air trapped in the system, a partially closed valve creating a Venturi effect, or a failing pump bearing.
• Root causes: Air ingress from a leak, automatic air vent failed, valve partially closed, or pump bearing wearing out.
• Fix: Bleed radiators first. If noise persists, check for closed valves, then call for pump inspection.
• Cost: Air bleeding — free DIY. Pump replacement $400-$700.

Gurgling / Water Sounds

Gurgling or water dripping sounds usually mean air or condensate issues.

• Cause: Air trapped in radiators or pipework, or condensate trap partially blocked.
• Fix: Bleed all radiators starting from the lowest floor. Check condensate drain for blockages.
• If water is brown or murky when bleeding: System sludge — needs power flushing.

Vibrating / Humming

A constant vibration or hum that you can feel through the boiler casing.

• Cause: Loose mounting bolts, failing pump, or pipework vibrating against walls.
• Fix: Tighten casing screws first. If vibration persists, pump may be failing — call for inspection.

Ticking / Clicking During Operation

Regular ticking during burner operation is normal — it's the ignition electrode sparking. But loud or irregular clicking is not normal.

• Cause: Normal — ignition electrode sparking. Abnormal — electrode arcing to ground, failing ignition transformer.
• Fix: If ticking is louder than usual or irregular, have the ignition system inspected.

Frequently Asked Questions