Diagnosing The Boiler Noise: Kettling

Any unusual new sound in the home can be stressful, especially if it’s coming from your boiler. One common and concerning noise is when your boiler sounds like a boiling stovetop kettle — known as kettling.

But what is boiler kettling, and should you be concerned?

What Is Kettling, And Should You Be Concerned?

For those who have never heard of the term (kettling) or the actual noise, don’t panic. If this is your first time hearing such a noise, it is a common issue, and we can only assume you have had your boilers serviced regularly.

For those looking to dial 999, there is no need to, as many boiler safeguards are in place to prevent extreme problems.

However, if the boiler in question is incredibly old, be sure to turn it off and contact a Gas Safe registered engineer to repair the issue.

But what exactly happens when your boiler kettles?

What Happens When Your Boiler Kettles?

While the name “boiler” suggests it will boil water, it should never do so. Your home’s boiler is designed to heat and maintain its water supply below boiling point.

Generally, for your boiler to kettle, there must be some sort of internal blockage inside your home’s heating system. When the water in the system starts to slow down or stop, it gets warmed up for longer, allowing it to reach a higher temperature and potentially boil.

The kettling noise you hear occurs when steam from the boiler escapes through an openings somewhere along its system or from the unit itself.

While kettling isn’t dangerous if it occurs for a short period, if left, it can damage your boiler\’s system and become hazardous. An example would be a sudden release of steam when someone is nearby.

Diagnosing Your Boiler Is Kettling

To ensure you’ve diagnosed your boiler correctly for kettling, there are a few symptoms you are looking for, and include the following:

The Noise

While it may seem the only noise associated with kettling would be the squeal itself, it can also be heard as:

• Whistling
• Popping
• Banging
• Rumbling noise
• And more depending on your boiler

Hearing any of these noises with the kettling sound will strongly indicate that it is the problem. Also, make sure the new noises occur when your boiler is operating.

But you must tick off a few more symptoms to be 100% sure of your diagnosis.

Water Temperature And Pressure

As blockages and the escalation of heat within the system cause kettling, you will also see changes in pressure and temperatures.

If the pressure within your system is high, it can indicate a blockage. Healthy boilers operate at a pressure of between 1 and 1.5 bars, but refer to your unit’s manual to check its optimal operational level.

Temperature-wise, if your thermostat is reading higher than you set it at, it indicates a problem.

Hard Water And Limescale

According to a report by the Drinking Water Inspectorate, around 60% of the UK has hard or very hard water.

Hard water contains high levels of specific minerals, namely magnesium and calcium. Over time, these minerals form a layer inside pipes, kettles, and boilers called limescale.

If you live in an area known for its hard water, forgetting to treat or descale your system to prevent limescale build-up could cause potential blockages and boiler kettling.

Now that we’ve reviewed the symptoms of a kettling boiler, what causes it?

What Causes Boiler Kettling? And Solutions

There are several common causes for a boiler to start kettling. We’ve skimmed over these causes in our diagnoses section above, but let’s elaborate below with some solutions as well:

Limescale Build-Up

As mentioned, limescale is caused by hard water, which is H~2~O with a high concentration of magnesium and calcium.

When hard water is heated, minerals are left behind and stick to internal surfaces. Those who live in hard water areas will be familiar with this.

If you don’t descale your boiler’s system, limescale can form a thick, crusty layer that will slow or block the water flow.

Also, limescale build-up can reduce heat transfer efficiency, depending on where it forms. This reduction in efficiency will lead to higher energy bills. It’s also worth mentioning that your boiler’s water will be noticeably colder if this happens, but no kettling.

However, if the limescale restricts water flow in certain areas in the system, the trapped water can overheat. This overheating produces steam, leading to a rumbling or “kettling” noise.

To remedy a boiler system with a limescale issue, there are several solutions:

Install Water Softeners

Water softeners are devices designed to reduce the mineral content of water, focusing on removing calcium and magnesium.

The most common water softeners in the UK use an ion exchange process to remove calcium and magnesium ions.

Add A Chemical Descaling Solution

If you do not have the capital to install a water softener, you can always add a chemical descaling solution. This solution will help break down and remove the limescale buildup.

The last solution is to ensure a Gas Safe registered engineer conducts your annual service and addresses the limescale issue.

Also, this is the last resort solution for all the problems causing your boiler to kettle.

Another issue that can cause blockages in your boiler’s system is sludge.

Sludge Build-Up

For those unfamiliar with sludge, it is debris that accumulates in boiler systems over time. Sludge can be a mixture of rust, dirt, and anything else that sneaks in.

Over time, components in your boiler’s system can corrode, releasing rust into the circulating water supply.

If not treated, it can thicken and obstruct the water flow, as limescale can. The signs you have a sludge build-up vary and include:

• Radiators with cold spots at the bottom
• The boiler is making a banging or knocking noise
• Energy bill increases
• And the colour of the water in your bled radiators is brown or murky

To fix a sludge build-up, there are a few solutions:

Magnetic Filters

Installing a magnetic filter will help capture floating metal fragments before they settle to the bottom with the rest of the sludge.

Chemical Inhibitors

Most Gas Safe registered engineers will add a chemical inhibitor to prevent corrosion and slow sludge formation.

Or, in extreme situations, you will need to have an engineer do the following.

PowerFlush

A Gas Safe registered engineer can perform a PowerFlush as a last-ditch attempt to clear your boiler’s pipe network.

Your engineer will attach a specialised machine to your boiler’s system that shoots a high-pressure water jet. This water jet dislodges the sludge and accumulated debris from your system.

A Leak

A leak is arguably one of the most common causes of a boiler starting to boil. When your system loses water, its pressure will begin to drop. The pressure drop and lower water level mean the boiler heats up quickly, forming steam.

Also, a leak can allow air to slip into your system and trap it. The trapped air can cause a system blockage, leading to pockets of water becoming overheated and turning into steam.

Lastly, depending on the size of the leak, it can cause water flow disruptions, which allows for local overheating and kettling.

Finding a leak in your system is one of the major tasks in solving this kettling issue. Fixing it can be tricky and requires a Gas Safe registered engineer.

However, you can help by looking around your home for the following signs of a leak:

• Checking visible pipes and joints for signs of water
• Looking for damp areas around the boiler or radiators
• Monitoring the boiler’s pressure gauge for drops in pressure

When the leak is located and repaired, your kettling problem should be solved — unless the next culprit causes it.

Faulty Thermostat

Yes, a faulty thermostat can cause or contribute to your boiler kettling. If your thermostat isn’t able to get an accurate temperature reading, it can lead to water overheating.

If your thermostat is acting up and overheating the water it will generate steam bubbles within the system, and when allowed, escape the system generating the kettling sound.

While, this situation would occur if the thermostat can’t detect the heat of the water, however, if it is inconsistently getting the correct reading it can heat areas unevenly. These fluctuations, or the boiler’s pilot light going on and off, can overheat water in isolated areas – generating steam.

But sometime, there’s nothing wrong with the thermostat and you’ve just set it too high. As a rule of thumb, your central heating temperature should be around 65°C to 70°C. If your home is well insulated, try lowering the temperature to 60°C.

While the ideal temperature for hot water is also 60°C. This is warm enough to prevent the growth of bacterial, such as Legionella, but won’t burn homeowners trying to take a relaxing shower.

Low Flow Rate Due To Broken Pump

A faulty boiler pump can contribute to it kettling. The boiler’s pump is responsible for circulating the water throughout the system. A broken or weakened pump will slow the water’s flow rate.

As we’ve mentioned, slow water tends to heat up faster, and when flowing at the correct rate will stop hotspots.

If your pump isn’t working correctly, signs include, other than a kettling noise are:

• Inconsistent heating
• Noise from the pump, which will sound like a whining or buzzing noise directly from the pump itself
• And frequent overheating or shutdowns of the pump itself

While there are not many DIY solutions, you can double check your boiler’s flow rate. Depending on the boiler’s size, type, and make, these optimal flow rates can fluctuate between 8 to 12 litres per minute.

Refer to your boiler’s manual for confirmation.

But generally, by ensuring your boiler is properly serviced annually by a Gas Safe registered engineer will prevent your boiler from kettling in the first place.

So, where can you book an appointment with a Gas Safe registered engineer?

Contact WarmZilla For A Gas Safe Registered Engineer In Your Area!

Worried about the noise? You can book a repair with WarmZilla. We can have a Gas Safe registered engineer to your home in 48 hours!

Simply follow the instructions on our boiler service page. And if you need additional help, you can talk to one of many experts.

If you have a sneaking suspicion that your boiler is over the hill, you can do our boiler survey which will suggest the perfect boiler for your home.