My boiler makes banging noise: How to fix it


If you have ever wondered why your boiler makes noise, we have written this article especially for you. There are several reasons why a boiler may be making noise, and here we will go through them point by point. Good boiler technicians (like doctors) often know how to define what kind of problem a boiler has by interpreting the noise it makes. In this article we also include a summary table with the causes of noise in a boiler and their respective solutions, as well as what to do when a boiler makes a loud noise.

Why is your boiler making noise

Any boiler of any brand can produce noises of various kinds. Some of these noises are part of normal operation, and you will gradually learn to recognize them:

  • The normal sound of water entering the system when you open the fill valve.
  • Since this is a pressure-driven device, it’s normal to some extent for it to emit sounds.

However, modern boilers are usually designed to operate with minimal or no noise. This means that most of the noise emitted by the boiler is the result of malfunctions or breakdowns. Let’s look at this in detail.

Why does your boiler emit sound? Summary table

Let’s first look at a summary table with the reasons why the boiler sounds. After this summary table, we will go on to look at some of the points and solutions in more detail.

It is normal for the boiler to make small sounds when you turn on the heating, as it is building up pressure within a closed hydraulic system.(This is not a problem and does not require a solution.)
It’s normal for the boiler to make some noise when you are filling the system with water to normalize the pressure.(This is not a problem and does not require a solution.)
If the noise is excessive during filling, it may be that the hydraulic system of the house has excess pressure.A household faucet should be opened during filling, or better yet, a plumber should be called to repair the excess pressure.
The expansion chamber is faulty and is not absorbing pressure surges as it rises.The expansion chamber must be repaired (fix the broken membrane or fill it with air), although the best solution is to replace it.
The normal boiler pressure is between 1 and 1.5 bar. When there is excess pressure, the boiler may beep when expelled due to leaks or the safety valve.Reduce pressure by removing water from the system (through radiators or discharge valve). Fix pressure problems.
General vibration noises, which may be transmitted to walls or pipes. They happen especially in older models of boilers.The boiler may be out of adjustment, misadjusted, with loose or expired parts. A plumber should be called in to make a general adjustment to the equipment, or it may be time to replace the old boiler with a new one.
The boiler makes beeping noises because the primary heat exchanger or the toilet is dirty or faulty.You must clean the piece, or replace it if necessary.
Air has entered the closed heating system and this causes hissing noises, echoes, etc.Purge radiators and/or boiler.
The Junkers boiler makes a noise similar to an explosion (this is true for other brands as well).The electrodes are defective and need to be replaced.
The boiler makes loud popping or beeping noises.The burner is dirty and needs to be cleaned.
When there are mechanical noises, the water circulation pump may be clogged or faulty.The circulation pump must be unclogged or replaced.

Your boiler makes a loud noise

If the boiler makes loud noises, this may be due to the same reasons we have seen so far, but also to others. When the malfunction is due to a dirty burner, the boiler may make noises similar to small explosions, and sometimes they will be like beeps. This is solved by cleaning the burner and servicing it. But it may also be necessary to calibrate the combustion, so that there isn’t any excess air.

What is a boiler heat exchanger?

One of the reasons why a boiler may rattle or make noise is because of dirt, malfunctions or breakdowns in the heat exchangers. Sometimes hot water generates foam or mineral residues that foul or damage the exchangers. Hard limescale can become encrusted in the boiler, especially in regions with hard water.

This may be aggravated when people apply the phony solution of adding dishwasher detergent to the system, following the myth that detergent reduces noise, when in fact it can produce noise. The noise produced by dirty or faulty exchangers can be similar to beeping. The solution to this is to clean the exchangers, or replace them with new ones.



Why is the radiator making noise?

Another cause of boiler noise is the radiators. Radiators make noise for two reasons, and each requires a different solution:

1. The radiator makes noise when there is air in the system.

When air has entered the heating system, both the system and the radiators tend to emit noises, sometimes very strange noises (hissing sounds, echoes, etc.) that people tend to associate with “horror movies”.

This only happens in the heating installation, which is hermetically sealed. The domestic hot water (DHW) installation is open, so it doesn’t cause this kind of problem. Air accumulation will also not occur if you consider installing automatic bleed valves in the radiators and boiler.

The solution to a noisy heating system and radiators is to purge both the boiler and the radiator emitting those noises, although it may be best to purge all radiators in the system.

To purge you must wait until the boiler and the system have cooled down (since this is what drives air and water apart). You need to start the process with the radiator closest to the boiler, advancing towards the farthest. If the house has more than one floor you need to start on the tallest floor and then go down. See more details in our tutorial.

2. The radiator makes a noise when there is sediment inside it

Another answer to the question of why the radiator makes noises is that it may contain water sediments. All equipment that works with hot water is prone to accumulate sediments and minerals that the water brings or generates (mainly magnesium and calcium).

In these cases, the solution is to disassemble the radiator and clean the inside, via the simple method of inserting a hose with pressurized water into the radiator inlet (the higher the water pressure, the more effective the cleaning will be). You’ll notice that the sediments are expelled through the radiator outlet.


If the sediments and minerals won’t come out with water pressure, this is a sign that they have become encrusted inside the radiator. Then it will be necessary to soften the sediments first, before removing them. You can do this by introducing plenty of white vinegar into the radiator and letting it sit for a few hours. After this, when you pour in the water, the mineral residues will come out.

If the Junkers boiler makes some noise…

If at some point you hear an explosion-like noise (and we say “explosion-like”, because in this case it’s not a real explosion), this may be due to faulty electrodes, and not just dirty or misaligned with each other.

This is true for any brand of boiler, but especially if the Junkers boiler makes such noises. These noises may be accompanied by symptoms such as the equipment does not generate heating or DHW.

The best fix would be to replace the electrodes with good spare parts, as simply cleaning or aligning them may not solve the problem. We recommend this solution to be implemented by qualified personnel. It’s not just a matter of removing the defective electrodes and installing new ones. The electrodes have to be installed at a specific angle to each other, and at a specific distance. Otherwise they will not work or will malfunction again.



Why is the heater making a strange noise?

Answering the question of why the heater might be making strange noises is a bit off the topic of this article. But we wanted to touch on this point here, at least in passing, because it actually has a lot to do with what we have been talking about. A heater can make a weird noise for a variety of reasons, which involve different solutions:

  • The tank (if there is one) may have developed limescale or residues which, when the water heats up, collide with the metal walls and produce noises. In these cases the solution is to purge the tank.
  • If the heater is making vibrating sounds (which may even be transmitted to the walls), it may be due to a general maladjustment. A technician can adjust and calibrate the parts, so that the equipment does not vibrate.
  • If it’s making explosion-like sounds but in cycle, it might be because there’s excess air inside the combustion. A plumber needs to adjust the burner.
  • If the heater makes hammering sounds, this is a sign of pressure surges. This should also be adjusted by a plumber.

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