Tankless Water Heater Making Noise? 6 Sounds and What They Usually Mean
A tankless water heater making noise is not always a fault. A unit with a fan, a burner and a circuit board makes some sound whenever hot water runs. What matters is a sound that is new, louder than it used to be, or one that arrives with a code, a temperature swing or a drop in hot water.
Six sounds follow, with what usually sits behind each. These are the likely suspects, not a diagnosis, and a technician listening with the cabinet open can tell for sure. If a noise comes with a smell of gas, get out and call the gas utility from outside. Otherwise, if it is getting worse, get a technician out.
1. A steady hum or whoosh while water runs
A gas unit has a fan and a burner, and both are audible when hot water is running. A steady hum or whoosh that sounds the same as it always has, and that stops soon after the tap closes, is normal. It can get louder when two taps run, because the unit is working harder.
A sound with no tap open needs a closer look. Units with a recirculation pump or built-in freeze protection can start up without anyone asking for hot water, and your manual says what yours does when it is idle.
2. Rumbling or a kettle-like sound
Scale narrows the waterways in the heat exchanger and insulates the metal, and a scaled unit can sound like a kettle coming to the boil. The other signs are swings between warm and hot, lukewarm water and overheat codes such as Navien's E016. A flush is the fix, and the guide to flushing a tankless water heater covers it. A unit that has never been flushed on hard water is the likeliest to do this.
3. Whistling or squealing
A whistle is usually water squeezing through a restriction: a clogged inlet filter, scale, or an isolation valve that was left partly closed after servicing. Check that the hot and cold isolation valves are fully open, clean the inlet filter with the unit off and the water closed, and see whether the sound changes. If it does not, the restriction is inside the unit or the pipes, and a technician should look.
4. A roar or 'jet engine' sound
A fan pushing hard against a restricted intake or exhaust can sound like a jet. Look at the outside termination for a nest, leaves or snow, and clear what you can by hand. If the roar continues, or a code such as 10 or E110 follows, stop and call. Fans, vents and combustion are technician work, and a failing fan is one of the part repairs on the usual list, estimated at $150 to $800 depending on the part.
5. Clicking, ticking or rapid on and off
On many units a run of ticks before the burner lights is the ignition at work. Repeated ticking that never ends in a flame is a failed ignition, and the guide to a tankless that won't ignite covers it. Clicking that comes with the unit starting and stopping while a tap runs steadily points at low flow or the flow sensor, and the guide to a unit that keeps shutting off has the checks.
6. Banging, knocking or vibration
A bang when a tap or valve closes fast is usually water hammer in the house pipes rather than the unit. Loose pipes make it worse. One forum reply on a new installation said the pipes should be strapped to the wall at regular intervals, about every six feet. Rattling from the unit itself can mean a loose mount or a fan problem. Either one is for a plumber or a technician to secure, not something to tighten blind.
When a noise means call
A noise that is new, louder than last month, or paired with a code, swings in temperature, a drop in hot water or any water around the unit deserves a visit. A diagnosis is estimated at $100 to $250, part repairs at $150 to $800 and a descale at $150 to $350. A written quote comes before any work, so you know what the noise will cost before you agree to it.
Quick answers
Should I be worried if my water heater is making noise?
A steady hum while hot water runs is normal for a unit with a fan and a burner. Worry about sounds that are new, louder than before, or that come with a code, temperature swings or less hot water.
Why is my tankless water heater humming?
A hum is usually the fan or the burner running, which is normal during a hot water draw. If it is louder than it used to be, or carries on long after the tap closes, have it checked.
Why does my tankless water heater make noise when the water is off?
Some units run a recirculation pump or fire their freeze protection without a tap open. If yours does neither and still makes noise, note when it happens and call.
Why is my tankless water heater loud and vibrating?
Water hammer in the pipes, loose pipe straps, a loose mount or a fan problem are the usual suspects. Heavy vibration with a code or a burning smell means switch it off and call.
Still no hot water?
A technician who works on tankless units can test it and price the fix in writing.
