Why is my tankless water heater making noise?
Tankless water heaters aren’t silent, but they should run with a consistent, low-level hum and a soft click when they ignite. New or louder sounds usually mean a component needs attention.
Each type of noise, clicking, rumbling, humming, or whistling, tends to point to a different cause, from harmless ignition to scale buildup or airflow restriction.
HeatLand has maintained tankless systems across Metro Vancouver and the Fraser Valley since 1999. Below we decode the common noises so you know what’s normal, what’s fixable, and when to call a licensed technician.
Clicking and Humming: Usually Normal, Sometimes Not
A light clicking when hot water starts is typically the igniter firing and the gas valve opening; this is normal and happens each time the unit starts. However, rapid or continuous clicking that doesn’t lead to ignition can indicate a faulty gas valve, a failing relay, or an ignition problem worth investigating. A steady hum usually comes from the internal fan or combustion blower and is normal operation. If the hum becomes loud, rattly, or vibrates the surrounding cabinet, a loose mounting bracket, a failing fan bearing, or a component vibrating against the housing may be the cause. Tightening loose fasteners can quiet minor rattles, but internal fan or valve issues need a technician. Note when the noise occurs, at startup, during heating, or after shutoff, since timing helps pinpoint the source. If clicking is accompanied by a failure to ignite, treat it as an ignition fault and book service.
Rumbling and Popping: Scale Buildup
Rumbling, popping, or crackling sounds almost always point to mineral scale on the heat exchanger. As water heats, it gets trapped beneath scale deposits and forms steam bubbles that collapse loudly, similar to a kettle furring up. Beyond the noise, scale reduces efficiency, causes uneven heating, and can trigger overheating lockouts. The remedy is a descaling flush with a manufacturer-approved solution, ideally done annually. If your unit hasn’t been flushed in over a year and has started rumbling, scale is the most likely cause. A HeatLand technician can perform a full descaling and inspect the exchanger for damage. Regular flushing not only silences these noises but also protects the unit’s efficiency and lifespan, and it helps maintain warranty coverage on many models. If rumbling continues right after a flush, the exchanger may need closer inspection for scale that has hardened or for early signs of damage.
Whistling, Screeching, and When to Stop
A whistling or high-pitched screech usually means air or water is being forced through a restriction, a partially closed valve, a clogged inlet filter, a restricted vent, or debris in the lines. Cleaning the inlet screen and confirming all service valves are fully open often resolves it. Airflow whistling from the venting can indicate a partial blockage that also affects combustion. Safety note: certain noises demand immediate attention. A loud bang or boom on ignition can signal delayed ignition and unburned gas igniting at once, which is a safety concern. If you hear banging on startup, smell gas, or notice sooting, shut the unit off and call a licensed gas technician; do not keep operating it. HeatLand’s TSBC-certified team can safely diagnose combustion-related noises, clear venting restrictions, and service valves. When in doubt about any loud or new noise, it’s safest to have it inspected.
Quick Checklist
- Note the type and timing of the noise
- Confirm all service valves are fully open
- Clean the cold-water inlet filter
- Schedule a descaling flush for rumbling or popping
- Tighten loose mounting hardware for rattles
- Stop use and call a pro for banging on ignition
| Noise | Likely Cause | Action |
|---|---|---|
| Light click at startup | Normal ignition | No action needed |
| Rumbling / popping | Scale buildup | Descaling flush |
| Whistling / screech | Restricted flow or vent | Clean filter, open valves |
| Bang on ignition | Delayed ignition | Stop use, call technician |
Frequently Asked Questions
Is a clicking sound from my tankless heater normal?
A single soft click when hot water starts is normal ignition. Rapid or continuous clicking that doesn’t result in the burner lighting, however, can indicate a faulty gas valve, relay, or igniter. If clicking comes with a failure to produce hot water, treat it as an ignition fault and book a licensed technician.
Why does my tankless heater sound like a kettle?
Rumbling, popping, or kettling sounds are classic signs of scale on the heat exchanger, where trapped water flashes to steam and collapses noisily. Beyond noise, scale hurts efficiency and can cause lockouts. An annual descaling flush usually silences it. HeatLand can flush and inspect your unit across Metro Vancouver.
When is a tankless heater noise an emergency?
A loud bang or boom on ignition, especially with a gas smell or soot, can mean delayed ignition of unburned gas, which is a safety hazard. Stop using the unit, avoid flames and switches, and call a licensed gas technician. HeatLand offers emergency service for combustion-related concerns.
Reviewed by the HeatLand Heating & Cooling team — licensed HVAC contractor serving Metro Vancouver & the Fraser Valley since 1999. This article is for general guidance only. If you smell gas, suspect a carbon monoxide leak, or are unsure about any electrical or gas component, stop troubleshooting immediately and call a licensed technician or 911.