Boiler Is Making a Banging Noise: Why, and How to Fix It

Tuesday 2nd November 2021
by Homeforce

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Tue 2nd November 2021

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As home appliance care specialists, we’re often called by customers stating their boiler is making a banging noise. Often it’s the best way of describing the noise a boiler makes when there is something wrong.

In truth, the noises can vary depending on the cause, but this description helps us too, as it means it could be due to a few issues. In this article, we’re going to help you diagnose, assess and take action to resolve the problem – one way or another. Let’s start with a quick roundup…

Your boiler is making loud banging noises – probably be due to a faulty thermostat or a build-up of debris on the heat exchanger. In either case, a qualified engineer must carry out a power flush. Other causes could be pipes with trapped air or trapped water, which you may be able to fix yourself.

Often issues with the boiler can be dealt with quickly with a plan to deal with them. Or, you can also read more about whether you can service a boiler yourself.

But to diagnose a boiler that is making banging noises, let’s first look more closely at the reasons it’s producing the banging noise in the first place. Later, we’ll cover a few other potential things it could be.

Your boiler is making a banging noise

Here are the main reasons your boiler will be making a banging noise.

1. The thermostat isn’t working correctly

If your boiler’s thermostat is faulty, it will not provide enough heat into the system for efficient operation. The water level in the tank might rise excessively or drop too low as a result of this.

When the temperature rises above 100°C, the excess pressure causes the water to expand. This results in the water banging against the sides of the tank.

This can sound pretty concerning, as the noise can often be loud enough to resonate around the home. And it is something that needs to be addressed as quickly as possible.

Failure to fix this issue soon could result in damage occurring in the internal workings of the boiler …that may then need to be replaced.

2. Limescale air vent blockage

This occurs when limescale builds up inside the boiler and blocks the air vents, or inhibits the heat exchanger part of the boiler’s internal workings. This can cause the boiler to overheat and subsequently shut down.

If the boiler overheats, it will shut off automatically. In this instance, you can diagnose this further by checking the temperature gauge to ensure the boiler is not getting too hot.

The most common reason for your boiler pressure to below is either a water leak somewhere in the system or reduced system pressure as a result of bleeding a radiator

3. Pipes might be the issue

The sound might be deceiving, and it could be the pipes …which we’ll explain more on later. So it makes sense to explore where the noise is originating from.

Let’s go through the steps to identify the root cause.

Steps to identify the problem and action

Step 1: Identify the source of the noise

Step 2: Diagnosis based on the type of noise

Step 3: Fixing the root cause

So take a closer look at the boiler itself, as well as the pipes flowing into and out of the surrounding boiler space.

A rushing water sound, for example, might be the result of an overflow pipe. So this is something you should also check. Here’s how to check and assess your overflow pipes.

Step 1: Identify the source of the noise

This is about tracking down the source of the noise. It’s all part of making a wider assessment of the problem. So firstly, it’s important to identify exactly where the noise is originating from.

It might be your boiler making a loud banging noise, or it might be noise reverberating from other areas and parts – such as a radiator or central heating pipe.

Often at this point, sounds that you might hear all the time start to be accentuated and you begin to listen more carefully, and you then suspect those as being the problem.

For example, creaking sounds may just be the result of pipes changing temperature – this is perfectly normal for pipes and happens all the time. So try to look for the more unusual sounds.

Once you’ve identified where the noise is coming from, you’ll then be able to diagnose what the problem is with greater accuracy. The next step is to exactly understand the type of sound it’s making…

Step 2: Diagnosis based on the type of noise

The next step is to identify what type of noise your boiler is making.

Often, diagnosing quickly and taking action where possible – based on unusual noises – can then help the further steps towards fixing the issue, helping to minimize complexity and potential cost

You may even negate the need for a replacement boiler. Here’s also the stress-free way to avoid boiler costs.

If ultimately you’re unable to diagnose and assess the noise, then you can always call upon a gas safe registered engineer to repair the issue.

Step 3: Fixing the root cause

In most cases, a banging noise emanating directly from the boiler is going to require some professional attention.

There are other noises that can potentially be fixed yourself, and we’ll go through those below based on what the noise is, but those that are related to loud banging coming internally from the boiler will require a qualified engineer to fix them.

To quickly deal with these issues in the future, why not consider cover for your boilerand your plumbing too, this provides fast repair services, and ultimately peace of mind that you’re covered. So you won’t have to worry …whatever the noise is – a quick call means someone will fix it for you.

Interpreting and diagnosing based on the type of noise

Before you get to that point though, here are some simple steps you can take to discover the root cause of the problem. Starting with the types of noises you’re hearing.

Loud banging noises

As we outlined earlier, loud banging noises are often the result of a faulty thermostat, limescale or debris build up in the system. Both of these sounds will likely require an engineer to call out for a repair.

Regardless of what it is from the above, it’s important that you turn off your boiler as soon as you suspect this is the case.

Whatever the cause of the banging, it isn’t good for your system and shutting it down is the best thing you can do.

Call on a professional to look at it as soon as possible, they will be able to eliminate the cause of the noise and assess it for repair or replacement.

Gurgling noises

Trapped air in the system can create the bubbling and gurgling noises you hear in radiators. Other causes could be low water pressure or a frozen condensated pipe.

Gurgling in a boiler is fairly common for most boilers. A small amount of air can often find its way into the system.

But it’s important to investigate further if this becomes an increasingly louder or constant noise. Usually, there are a few simple fixes that can be carried out by yourself at home – depending on the issue.

Whistling or kettling noises

Perhaps the sound is familiar to you, as it emulates that of a whistling kettle. If so, this issue is commonly referred to as kettling – obviously!

Commonly, the cause of boiler kettling tends to be as a result of an accumulation of limescale on or around the boiler’s heat exchanger.

Often this happens in hard water areas.

Depending on where you are in the UK, might determine if you’re within a hard water area or not. Hard water is a term used to describe H2O that possesses high mineral content such as calcium and magnesium. It isn’t necessarily better or worse than soft water, it just contains a higher level of minerals.

Places such as London, Southampton and Bristol are known to have a higher than average degree of hard water, ranging from hard to very hard.

Calcium is the main culprit in these circumstances. Because of calcium, limescale deposits often build up in layers over time which restricts the flow of water. Unfortunately, no boiler is immune to this happening.

Results in trapped water in the heat exchanger

The result is that water can become trapped within the boiler’s heat exchanger – which in turn causes it to overheat. This generates steam and therefore expands.

The whistling noise refers to the consequence of this process …as boiling air is forced through smaller gaps in the system – just like a boiling kettle. Often though this could also sound like a low banging or popping sound.

There are other variables on this theme too, such as debris or sludge collecting around the heat exchanger. Or possibly a pump that has become jammed and may need to be replaced.

Kettling causes reduced efficiency due to long-term damage caused to your boiler. Simply because more fuel is required to reach the required temperature. This naturally impacts your monthly energy bill.

Not only that, but you could significantly reduce the lifespan of your boiler.

Other reasons your boiler is making a noise

So we can provide the best resource possible, let’s go over a few other potential boiler issues or boiler noises you might be experiencing.

Water pressure or water flow is too low

When the water pressure or water flow is too low, water passes over the heat exchanger much slower than it should.

This slower speed causes the water to overheat, giving rise to steam bubbles that expand quickly and erupt once they contact cooler water.

The water temperature on the boiler is set too high

Boilers run better at an optimum temperature, and just because the temperature setting goes really high doesn’t mean you should run it at that level, at least not for extended periods.

Setting your boiler to a very high temperature can overheat the water, causing steam bubbles.

Banging pipes – air in the pipes

Often we interpret banging noises as coming from the boiler itself.

If for any reason air is able to find its way into the pipes, then it can cause fluctuations in pressure that can cause loud gurgling or banging noises, we’ve probably all hard these from time to time. With some closer analysis, you can trace this down to particular pipes or radiators.

Air can enter the heating system in a number of ways; Ranging from defective valves to parts that have previously caused problems.

This is especially common in boiler systems that feed through to radiators.

The best solution is to seek to drain all the air from the system. This enables the pressure to equalize again.

You can do this if you know what you’re doing. If not, then call out a professional to do it for you.

Here’s a table that outlines the range of boiler issues you might face, plus the likely cause and the remedy

Boiler noise issueCauseRemedy
Loud banging noiseFaulty thermostatEngineer call out, new thermostat
Loud banging noiseLimescale build-upEngineer call out, system flush
Loud or low banging noiseBoiler set too highReduce temperature settings
Insufficient water flowWater leakRepair water leak
Pipes bangingAir in the pipe systemBleed the system
Whistling / KettlingLimescale build-upEngineer call out, system flush

How to stop the banging noise?

If the noise is caused by a build-up of debris in the system, you will ultimately need to clear the debris. 

Depending on the make and set up of your central heating system means you need either a power flush or a chemical cleaner.

Power flush involves attaching a specialized machine to your heating system that pumps commercial grade cleaning chemicals around the system to flush out any blockages and general debris, followed by a fluid called an inhibitor to protect it from future build-up.

After an issue has arisen with your boiler, the strongest recommendation is to seek to cover your appliances against future issues. You can do this easily here, so you can give yourself peace of mind and remove any boiler-related anxiety in the future!

More boiler help…

You’re probably reading this article because there is a problem with your boiler. But this issue could happen to any number of appliance and home systems.

Ideally, you want to be able to deal with issues as soon as they arise. So click here to cover your boiler from future issues. Click here to cover your appliances, and here for your plumbing. Or simply contact us.

Ready to get started? Call us anytime on 0844 77 00 597 or

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