A heating system typically bangs because of expanding metal, trapped air in the water lines, or a delayed ignition. The exact cause often depends on whether you have a forced-air furnace, a boiler (radiator) system, or an issue with your ductwork.
Banging pipes (often called "water hammer") are a warning sign of a plumbing issue. While the noise itself is just annoying, ignoring it can overstress pipe joints, wear out valves, and eventually cause leaks or burst pipes.
Banging Sounds
Oftentimes, this sound is caused by a buildup of gas within the furnace's combustion chamber, resulting in a miniature explosion inside your heating system when the unit does light. Sometimes this issue is caused by dirty ignitors, a clogged burner, gas pressure problems, or a weak pilot light flame.
It's easy to avoid this problem by regularly changing your furnace filter. Our HVAC technicians suggest replacing the filter once every three months or as soon as it's no longer a clean white color. If you have pets in the house, you need to change it every month.
Air in the system
One of the most frequent causes of banging noises is trapped air in your central heating system.
Your furnace should run quietly, with only a soft hum or gentle whoosh of air. But when that turns into banging, buzzing, or whistling, something inside isn't working the way it should. The most common culprits are loose parts, clogged filters, dirty burners, or electrical problems.
To diagnose and fix water hammer in a cold water system, check for air pockets or loose faucet washers, and consider installing a water hammer arrestor or expansion tank. "That's water hammer. Call a plumber (unless you're comfortable doing plumbing) you need a water hammer arrestor."
Although it can be worrying when your boiler is making loud noises, it's not usually a cause for alarm. This is because boilers have safety mechanisms that mean that the boiler will turn itself off before it can become dangerous.
Sudden banging pipes (known as "water hammer") are usually caused by high water pressure or the rapid shut-off of a valve in an appliance like a dishwasher, washing machine, or toilet. When the water stops abruptly, the kinetic energy creates a shockwave that violently rattles the pipes against wall studs.
A constant hissing or rushing sound, often coming from the walls or floors. Gurgling or bubbling sounds when using plumbing fixtures. Whistling or clanking sounds, which may indicate water escaping from a damaged pipe.
Hearing knocking in your walls at night is usually caused by thermal expansion of building materials, plumbing issues like "water hammer," failing exterior vents shifting in the wind, or nocturnal pests. These noises seem louder at night because ambient household sounds drop and the house cools down.
However, the loud bang or series of bangs or shuddering noises is normally more of a shock to a homeowner than the plumbing system. Don't panic. The sound is unlikely to damage your pipes and there is a relatively easy fix.
5 Warning Signs It's Time for Furnace Replacement
Listen for Banging or Clanking Noises
The sound is often created by high-pressure water moving through a compromised pipe, putting stress on the entire system. Ignoring these jarring sounds can lead to a full-blown burst.
Yes, water hammer can cause severe and expensive damage to your plumbing system over time. When a valve shuts quickly, the sudden stop of flowing water creates a high-pressure shockwave that slams into your plumbing. This forceful impact acts like a physical blow to your pipes.
In plumbing, the "135-degree rule" is a code standard that dictates how much a horizontal drain pipe can bend or change direction. It limits the total cumulative angle of pipe fittings before a system requires an access point (cleanout) or must be vented, ensuring proper flow and preventing chronic clogs.
The long-term effects of water hammer might present themselves in the following ways: Leaks: Water hammer has the potential to damage joints, fittings and connections, resulting in poor seals and ultimately leaky pipes. Ruptured pipes: Ruptured pipes due to built-up pressure can be particularly expensive to repair.
Identify older or worn out parts like the blower motor or fan that may need tightening or replacement. Replace a faulty gas valve or ignition system if these have been diagnosed as the cause of the banging noise. This will ensure safe and efficient furnace operation.
The heat exchanger is often considered the most costly part of a furnace to repair or replace. It is a critical component that transfers heat from the combustion process to the air that circulates throughout your home. Over time, heat exchangers can crack due to the constant heating and cooling cycles they undergo.
The $5,000 rule is a guideline to help homeowners decide whether to repair or replace their HVAC system. You multiply the age of your unit by the cost of the needed repair. If that number exceeds $5,000, replacing your HVAC system is often more cost-effective.
A heating knocking or banging noise is usually caused by thermal expansion (metal pipes expanding and rubbing against wooden floorboards or joists) or trapped air in your system. It can also be caused by loose pipe brackets or sediment build-up in older boilers.
To stop banging heating pipes, first identify whether you have a steam system, hot water (hydronic) system, or if pipes are knocking against floorboards and joists. Common fixes range from wrapping noisy pipes in insulation to adjusting the tilt of your radiators.
It could be a cracked heat exchanger, which can lead to carbon monoxide leaks. Call in a professional. Knocking is often caused by ductwork adjusting to hot or cold air blowing through. Rumbling sounds can mean the pilot light is improperly adjusted or dirty, or that the motor needs oil.