Troubleshooting Common Boiler Noises: What They Mean and How to Fix Them

Most UK homeowners are well acquainted with the sounds their boiler makes. Whether it’s the roaring sound of the pilot flame warming up water or its gentle hum while maintaining your home’s temperature you know the sound of a healthy boiler.

However when an unusual new loud noise starts coming from your boiler that you don’t recognise it often indicates something is wrong.

Can A New Loud Boiler Noise Be Dangerous?

While it can be incredibly worrying to hear a new noise bellowing from your boiler it can be alarming. But it is usually not an immediate cause for concern. All boilers sold in the UK must meet rigorous standards for efficiency and safety.

Boilers sold in the UK have built-in safety devices that ensure they are safe for use in your home. There are three critical safety devices:

Safety Valves

As mentioned in a previous blog the invention of safety valves in hot water boilers revolutionised the industry and the world.

Valves allow the release of built-up pressure if a failure occurs. By releasing this pressure the boiler protects itself from self-destruction. These simple valves have been perfected over the last century with the smallest design tweaks being implemented regularly.

However valves can become clogged if the boiler’s system is not regularly serviced (so make sure it is).

Another safety device is your boiler’s pressure gauge which will indicate whether there’s an issue.

Water-Level Control And Low-Water Fuel Cutoff System

While some boilers might install these systems separately they are now more commonly combined to function as one safety feature.

The water-level control system monitors the water level inside your boiler and maintains the correct level. If the water level drops too low the boiler will automatically shut down and give you an error code.

When the boiler shuts down it also cuts off the gas supply. Most boilers also have a water gauge indicator to give you an idea of their level.

Combustion Control Systems

Your home’s boiler heats water with a gas flame. It is important to remember that a balance between air and fuel needs to be maintained. Otherwise it can be a health problem.

A boiler’s pilot flame needs to be crisp blue. If it’s yellow or orange (sometimes called a floppy flame) it’s a sign of incomplete combustion caused by a lack of oxygen reaching the flame.

A floppy flame produces carbon monoxide (CO) which is odourless tasteless and poisonous. Your Gas Safe registered engineer must check the condition of your boiler’s pilot light.

Luckily combustion control systems ensure this isn’t a constant issue. Your boiler also has a ventilation system to ensure that nearly all byproduct gases are dealt with safely.

However make sure to install a working CO metre. If you suspect a gas leak switch off the appliance immediately and shut off the gas supply at the metre control valve.

Open all doors and windows to ventilate the gas out and call the National Gas Emergency Service on 0800 111 999.

Now that we’ve put your mind at ease it’s time to troubleshoot some common boiler noises.

Troubleshooting Common Boiler Noises

There is an extensive list of noises that are associated with boiler problems.

This list of noises includes:

• Kettling (like a stove kettle boiling)
• Gurgling
• Clicking or tapping
• Vibrating
• Buzzing or whining
• Whooshing
• Banging

Let’s review this extensive list to discover what could be wrong with your boiler.

Boiler Kettling

It can be extremely alarming to hear your home’s boiler starting to squeal like a stove kettle but it’s not an uncommon issue.

Your boiler makes this noise due to the slowing water flow. The slow-flowing water is heated faster than usual warming and boiling it.

The steam from boiling water forces trapped air out of the system generating a whistling sound.

As mentioned the kettling noise is caused by a slowing of water flow around your boiler’s system. This indicates either an issue with how water is circulated or a blockage.

If you hear your boiler creating a kettling noise it can be a severe issue requiring a Gas Safe registered engineer to fix it.

Common causes for kettling include:

• Limescale build-up
• Leaking system
• Problem with the thermostat
• Faulty water pump
• Or your boiler is overheating

For those living in an area with hard water the culprit is most likely limescale. Depending on the severity of the build-up an engineer might recommend performing a chemical clean or a Powerflush.

Or the engineer might recommend installing a magnetic filter.

While a kettling noise is usually an indicator of the mentioned issues it can also be heard as a banging sound.

Boiler Gurgling

Your boiler can occasionally make a gurgling sound. However if it makes this noise regularly you should investigate the cause.

The most common reason is that air is trapped in your radiators. But it could also be related to:

• Frozen condensate pipe
• Water shortage in the system
• Or a low water pressure

You can diagnose if any of the above mentioned reasons caused the issue visually.

A frozen condensate pipe will require defrosting it

A water shortage in the system can be seen via the boiler’s water gauge

And you can check your system’s pressure via the gauge

You must bleed your radiators if you have gone through this list and can still hear your boiler gurgling.

Bleeding your radiators is a simple task that should be done once a year.

To bleed your radiators you will perform the following steps:

1. Find Tools
   To bleed your radiator you will need your radiator key or a flat-head screwdriver (depending on the radiator) a towel and a small bowl.
2. Turn Off And Locate
   Turn off your heating system and let it cool down before you start working. When ready locate the radiator with the cold spot and its bleed valve usually on top of the radiator.
3. Bleeding The Radiators
   Open the bleed valve by turning it in an anti-clockwise motion using your radiator key or screwdriver. When it opens you should hear a hissing noise as the air escapes the system.

Sludge Build Up

Another cause for kettling or gurgling could also be sludge, sludge build up in your boilers heat exchanger leads to noises. A Powerflush will help with this issue.

Clicking Or Tapping

If your boiler consistently makes a clicking or tapping noise the issue is most likely with the pilot light. The clicking or tapping sound is usually the ignitor trying to spark your boiler’s flame.

In this situation you must call a Gas Safe registered engineer as the problem concerns the gas supply.

Vibrating Noise

For those being driven mad by a constant vibrating noise you could be lucky and just need to tighten a screw. In the best-case scenario you’ll be able to locate the loose screw and tighten yourself. Or in the worst case it’s inside the boiler which will require a visit from your Gas Safe registered engineer.

Another common culprit for causing a vibrating noise from your boiler is something trapped in your flue. If you can locate your flue and get close to it you will need to check if the gases are being expelled correctly.

It’s easy to test if the flue is blocked. Simply place your hand over the flue slowly and feel if there is a steady airflow coming out of it. If there is a blockage turn off your boiler and clear the flue from the gathered debris.

If a flue blockage isn’t the issue we’d strongly recommend calling an engineer to diagnose the problem as it could be several problems which include:

• Incorrect pump setting
• Residue on your heat exchanger
• Or built-up residue inside your boiler

Buzzing Or Whining

A buzzing or whining noise is usually associated with a worn bearing. When your boiler is operating at full capacity these bearings turn incredibly quickly.

If the bearing is worn it will make a buzzing or whining noise. To fix this issue you will need to call a Gas Safe registered engineer to locate the bearing and replace it.

Whooshing

A whooshing sound from your boiler is usually caused by a blocked air circulation system which is generally associated with combi boilers.

A blocked air intake pipe is typically located at the back of a boiler. This blockage is creating this loud whooshing sound. You can usually just reach over the boiler to clear the intake pipe.

However if the whooshing sound is inside the boiler your boiler’s air filter is blocked and you will need to call a Gas Safe registered engineer to replace it.

What To Do With A Dead Silent Boiler

The simple answer is to replace it. Luckily our WarmZilla survey makes selecting a new boiler easy.

If you didn’t find the noise your boiler is making on our list we suggest chatting to our expert consultants.