A boiler that suddenly starts banging, rumbling or whistling can be alarming, especially on a cold night. Some noises are normal, some mean your system needs service soon, and a few mean you should shut it down and call right away. Here’s how to tell the difference, from a NYC heating contractor who works on steam and hot-water boilers every day.
Shut it down and call now if you notice:
- A loud boom or “whoomp” when the burner lights. That’s delayed ignition, and it can damage the boiler.
- The pressure relief valve hissing or dripping water. It opens when pressure gets too high.
- A gas smell, or a carbon monoxide alarm. Leave the building and call 911 or your gas utility from outside.
Banging, clanking or knocking pipes
On a steam system, this is usually water hammer: water collects in pipes that should only carry steam, and the steam slams it along the pipe. Common causes are radiators or pipes that have lost their pitch, a boiler water level that’s too high, or failing steam traps. It’s one of the most common heating calls in older NYC buildings, and it’s usually fixable.
On a hot-water system, banging can come from pipes expanding as they heat, or from water flow problems. A pipe that knocks every time the heat comes on is worth a look.
Rumbling or “kettling”
A rumbling sound, like a kettle about to boil, usually means scale or sludge has built up on the boiler’s heat exchanger. Water gets trapped, overheats and boils in pockets. It makes the boiler less efficient and can shorten its life. A professional cleaning or flush often fixes it. Low water flow from a failing pump can cause it too.
Gurgling or bubbling
Gurgling in a hot-water system usually means air in the pipes. Bleeding the radiators often helps, but if the air keeps coming back, there may be a leak, low system pressure, or a problem with the air separator or expansion tank.
Whistling or hissing
On steam radiators, a gentle hiss from the air vent as the radiator heats is normal. A vent that hisses constantly, whistles loudly or spits water has failed and should be replaced. On a hot-water boiler, hissing from the relief valve is not normal. See the shut-down list above.
Humming, buzzing or whining
A steady hum or whine usually comes from the circulator pump, the burner motor or a fan. A pump that’s getting louder may be wearing out. Worth having checked before it stops and leaves you without heat.
Clicking, then nothing
Repeated clicking without the burner lighting usually points to an ignition problem: an igniter, flame sensor or control. If the boiler won’t light after you’ve pressed the reset button once, don’t keep pressing it. Call us.
Can I just live with it?
Some noises are just annoying. Others mean the boiler is working harder, wasting fuel or heading for a breakdown on the coldest night of the year. If a noise is new, getting louder, or comes with cold radiators, short cycling or water on the floor, have it checked.
Boiler making noise? We can help.
We service steam and hot-water boilers in homes, apartments, multi-family buildings and businesses across all five NYC boroughs. We find the real cause, show you what we found, and put the price in writing before any work. Call (212) 516-9632. Calls are answered 24/7, and no-heat calls get priority. See also: boiler service & repair and no heat? emergency heating repair.