Eco Happy (Solar Expert)

Published February 28, 2024

Is your boiler making unusual noises? Most modern boilers have been designed to run quietly, so a noisy boiler can indicate there’s a serious issue.

Unsure what’s causing it and what to do about it?

You’ve come to the right place!

We have plenty of experience with all of the issues that cause a boiler to start making strange sounds. So, we’ve created this guide to tell you what the most common causes are and what you can do about them.

Kettling Noises

When a boiler is “kettling”, it makes a combination of popping, whistling, bubbling, and rumbling noises while running. The three main causes of kettling are limescale buildup, overheating, and leaks in the boiler system.

  • Limescale buildup: This occurs when limescale accumulates within areas of the system causing blockages. Limescale buildup is fairly common in the heat exchanger.
  • Overheating: This causes the water in the boiler to turn into steam, resulting in strange boiler noises like whistling sounds.
  • Leaks: If a leak has developed somewhere in the system, it’s hard for the boiler to circulate water, producing strange noises.

What to do

If your boiler is making kettling noises as a result of limescale buildup, a power flush will most likely be required. Performing a power flush requires specialist equipment, so you’ll need to call a Gas Safe registered engineer to do it for you.

Likewise, if there are any leaks in the system, you’ll need an engineer to assist you. Or, you can learn how to fix a boiler leak by reading our comprehensive guide.

If the issue is overheating, you might just need to reset your thermostat or lower the temperature. However, if this doesn’t resolve the issue, you’ll need to contact an engineer.

Gurgling Noises

Gurgling noises are usually caused by a frozen condensate pipe, low water pressure, or trapped air.

What to do

  • Trapped air: If the gurgling sound is caused by trapped air, the issue can often be resolved by bleeding your radiators. To learn how to do this, check out our handy guide on how to bleed a radiator.
  • Low water pressure: To see if the gurgling noises are caused by low pressure, you’ll need to take a look at the boiler’s pressure gauge. If the dial is below 1 bar, the pressure is low. This means you’ll need to repressurise your boiler using the filling loop. Read the manufacturer’s instructions for how to do this.
  • Frozen condensate pipe: If this is the cause of your noisy boiler, slowly pour warm (not boiling) water over the pipe until it’s completely thawed.

Loud Banging Noises

Loud banging noises typically occur due to trapped air, kettling, limescale buildup, loose pipes, and faulty thermostats.

What to do

We’ve already covered how to resolve some of these issues, so you can follow the steps above for them.

However, if the loud banging noise is caused by a faulty thermostat, you’ll need to contact the manufacturer and request a new one. Hopefully, it’ll be covered under your warranty.

It may also be the case that your thermostat is simply in the wrong place. The best place for a thermostat is on an interior wall in the centre of the home, away from any obstructions.

If the noises are the result of loose pipes, you could try to tighten them yourself with a wrench. However, it’s usually best to contact a Gas Safe registered engineer to address this type of issue.

Rattling Noises

Rattling noises tend to be caused by excess air in the system or loose components in the boiler or central heating system. If it’s the latter, loose screws and other components can rattle as water is circulated through the system.

What to do

As with gurgling noises, if the issue is air trapped in the system, you should bleed your radiators.

If the problem is loose components, you can tighten them and see if the noises stop but it’s generally best to call a Gas Safe engineer to fix it for you.

Vibrating Noises

When your boiler is making vibrating noises, it’s typically a sign of a faulty pump, a blockage in the air intake flue, or worn-out components within the system.

What to do

  • Faulty pump: This will need to be either repaired or replaced by a Gas Safe engineer.
  • Air intake or flue blockage: First, check inside the flue for blockages and remove any that you find. If there are no flue blockages or the issue persists once you’ve cleared the flue, the problem is most likely with the air filter. In this case, you’ll need an engineer to assist you.
  • Worn-out components: A defective burner or worn vibrating fan bearings are often the cause of these noises. This is another issue that requires the expertise of an engineer.

Loud Humming Noises

If your noisy boiler is making humming sounds, it’s most likely due to an issue with the fan, limescale buildup in the heat exchanger, mains water arriving at too high a pressure, or a circulation pump that’s operating too fast.

What to do

None of these are issues that you should try to resolve yourself. If you do, you risk causing further damage to the boiler or central heating system. In these cases, call out an engineer.

Buzzing Or Whining Noises

The primary causes of buzzing or whining noises are defective burners or worn vibrating fan bearings.

What to do

Again, these issues can be dangerous to address yourself and you may cause further damage. So, call an engineer if your boiler is emitting buzzing or whining noises.

Clicking And Tapping Noises

The main culprits for clicking and tapping noises are air bubbles and a faulty ignition. The clicking noise may be the sound of the ignition attempting and failing to ignite. Or, it may be the sound of air bubbles expanding and contracting as they pass through the central heating system.

What to do

As with any issue involving air in the system, if the noises are the result of air bubbles, you should try bleeding your radiators to see if this resolves it. If it doesn’t, then the most likely cause is a faulty ignition and you’ll need to call an engineer.

Whooshing Noises

Whooshing noises are primarily caused by air filter blockages or air intake blockages. If the intake or flue is blocked, the boiler can start to vibrate and make an unusual whooshing sound.

What to do

Follow the steps for clearing flue or air intake blockages we laid out in the ‘vibrating sounds’ section. If this doesn’t resolve the issue, then you’ll need to arrange for an engineer to inspect your boiler.

How Often Should Your Boiler Be Serviced?

The best way to prevent any of the issues that cause strange boiler noises is to have your boiler serviced regularly. But, how often should a boiler be serviced?

Well, your boiler needs to be serviced once a year so that a qualified engineer can inspect it and deal with any minor issues before they become more serious.

An annual boiler service usually involves:

  • Internal inspection: The engineer will inspect the internal components of the boiler such as the burner, heat exchanger, and main injector.
  • External inspection: The engineer will visually inspect the exterior of the boiler and its pipes for any signs of leaks, damage, or corrosion.
  • Cleaning: Any soot, limescale, or general debris will be removed from the boiler’s internal components.
  • Flue checks: Any blockages will be removed from the boiler’s flue.
  • Emission checks: The engineer will check the levels of carbon monoxide and other gases being emitted from the boiler.
  • Efficiency testing: The engineer will use a flue gas analyser to evaluate the boiler’s efficiency levels and combustion. If needed, they’ll make adjustments to improve its performance.
  • Safety checks: Safety devices like the pressure relief valve and the thermostat will be checked to make sure they’re working properly.

It’s also important to bear in mind that most boiler warranties are only valid if the boiler is serviced annually.

Compare Boiler Installation Quotes With Eco Happy

Sometimes, the issues causing a noisy boiler are so severe that you’ll need to have it replaced with a new boiler. Besides the cost of the unit, this means you’ll also have to pay installation costs.

While this can be pretty expensive, you can save money by comparing boiler installation quotes with Eco Happy. In just 30 seconds, you can compare the installation costs of all the service providers in your area. You can then choose the best and most affordable deal for you.

FAQs

When is a noisy boiler dangerous?

Any unusual noise coming from your boiler could potentially be a sign of danger. For example, if the heat exchanger malfunctions, this could cause a carbon monoxide leak and fire hazards.

Whatever the noise, any issues with your boiler should be addressed as quickly as possible, whether by you or an engineer. If you smell gas at any point, evacuate your home immediately and call the National Gas Emergency Service on 0800 111 999.

How can I prevent the issues that cause unusual boiler noises?

Besides getting your boiler serviced annually, there are some other steps you can take to prevent the types of issues that can cause your boiler to start making strange sounds.

For instance, you could lag any external pipes to prevent freezing and add inhibitor tablets to your boiler system to prevent limescale buildup.

How much will it cost to have my boiler repaired?

This can vary widely depending on the type of issue, the type of boiler, and the service provider. However, it costs between £100 and £500 on average to have your boiler repaired. Emergency repairs cost around £410 on average.

Final Thoughts

When your boiler starts making unusual noises, it can be quite worrying. Many different things could be causing this to happen. Fortunately, many of these issues can be resolved by you. If not, the majority of boiler noise issues can be fixed fairly quickly by a Gas Safe Engineer.

Usually, strange noises aren’t a sign that your entire boiler needs to be replaced. They tend to be caused by relatively minor problems. Remember, the best way to avoid them turning into major problems is to ensure your boiler is serviced annually.

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