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Boiler Kettling Noise: How To Fix and Stop?


Homeowners describe the sound differently. Some say it’s a clang, others it’s a bang and others still a pop. But whatever term they use, the problem is the same – kettling. When the kettling sound is from a kettle, it’s rather comforting. But when it’s from the boiler, it’s alarming and a source of distress and anxiety for most homeowners.

The noise makes you question whether the boiler is operating efficiently and safely. There are many reasons why boilers produce a kettling noise. It’s essential to know them and deal with them appropriately. Luckily, the solutions are easy to handle with detailed instructions at hand.

5 common reasons for kettling and how to stop it

A leaking boiler system

In most cases, kettling is caused by boiler leaking. This could be a leak close to the boiler or along the system’s pipework. If you haven’t noticed a leak yet, you should inspect the entire system. Start the inspection with piping around the boiler – especially those under it. Later, inspect the pipework close and around the radiators. A leaking radiator could also produce kettling noises. During the inspection, be keen on the pipe joints.

Now, there are several reasons why your boiler could be leaking. It could be due to shoddy pipe installation, over pressurisation, and corrosion over time, among other factors.

Fixing a leak

Fixing a leak in the system can be done through different methods depending on the components and boiler spots involved in the leak. If it’s an external leak that is caused by a loose joint or a failed seal, the repair cost should be anything between £70 and £150. However, if the leak is internal, there’s a chance the problem is severe since some parts might be corroded. Because of this, the repair costs are about £300 and higher. And in some instances, a new boiler installation might be required.

If you have an old boiler, there are high chances the leak is caused by natural corrosion in the pipes and a host of other factors. In this case, we advise that you replace the boiler. Spending money on repairs will only solve the problem temporarily.

Limescale build-up

Another common cause of kettling is sludge and limescale build-up in the system. Boilers are designed to last long. However, with time, limescale can build up in the heating system. The build-up restricts and traps water flow. This is especially in the piping closer to the heat exchanger. When this happens, the system overheats and steams abnormally resulting in kettling sounds.

Limescale is the natural deposit of minerals (usually calcium and magnesium present in the water), on the walls of the boiler system. Different areas in the UK have different levels of minerals in their water. In areas served with hard water, the limescale builds up since hard water has higher levels of minerals. Soft water has lower levels of these natural minerals. Because of this, hard water areas are susceptible to limescale build-up than soft water areas.

If you are unsure of the type of water pumped in your area, you can confirm with your local authorities.

limescale clean solutions

Limescale build-up is best handled through a chemical clean or a power flush. You should hire an expert heating engineer for this. Chemical clean solutions are made from corrosive chemicals that only target limescale.

The common ingredient in these cleaning agents is hydrochloric acid. Once the acid reacts with the limescale, soluble salts and carbon dioxide is produced. Once introduced into the system, the chemicals are allowed to sit for a couple of hours or even days, depending on the extent of limescale build-up.

A power flush works in the same way. The only difference is that this process involves using a water pressure device to rinse off the limescale from the piping. The water is treated with a chemical solution to quicken the process. This fix will cost you anything between £250 and £400 depending on the size of the affected piping and the thickness of the limescale build-up.

When the limescale build-up is too thick for the above fixes, manual removal and cleaning is the only solution. Once this is done manually, the system is flushed for an even cleaner result.

Faulty thermostat

If your thermostat is broken or faulty, your boiler might be overheating and kettling. To confirm you have a faulty thermostat, check its settings and reset it accordingly. If you don’t know how to reset and adjust the thermostat settings, you can read through the boiler manual.

Fix your faulty thermostat

But if resetting the thermostat doesn’t fix the problem, you need to call in a professional to fix it for a fee (usually between £100 and £150).

Old boiler thermostats are easily given to problems. And though repairing the thermostat is an option, we advise replacing it altogether. Most boilers have a warranty of between 10 and 15 years. When they hit this age, they break down easily, and the repairs needed are expensive. As such, it’s more cost-efficient to have a new boiler installed. A new boiler will come with the added benefit of saving energy.

Incorrect boiler pressure

Though every boiler has its predetermined normal pressure, the normal range is between 1 and 2 bar. The exact boiler pressure is visible on the pressure gauge that’s located on the control panel. Boilers are created to balance their pressure. But occasionally, the pressure deviates from the normal by decreasing or increasing. These abnormal pressures can cause kettling.

A leak in the system often causes low boiler pressure. And aside from creating boiler noises, low boiler pressure makes the system inefficient and the energy bill skyrockets. Luckily, solving low pressure in a boiler is easy.

You can repressurize the boiler system. You can do this using the following steps

  • Locating the pressure gauge and the filling loop. Filling loop handles are usually positioned at 900 to pipe flow.
  • When accessing the boiler filling loop, make sure you can view the pressure gauge. The correct pressure should be in the green zone. In the absence of a green zone, check the boiler manual for the recommended pressure.
  • Before you start the process, turn off your boiler
  • Turn the filling loop handles 900 to align with the direction of flow in the pipes. Once this is done, you should hear the water flowing through the pipes
  • Once the pressure is adjusted to correct levels, turn the filling handles back to their original position.
  • Turn on the boiler

If the pressure drops again, take it as a sign of a deep-rooted boiler system problem

When the boiler pressure is high, depressurising it should work. Though boiler pressure rises when the boiler is on, it shouldn’t go outside the 1 and 2 bar range. Anything higher than this puts the boiler at the risk of shutting down. To fix the problem, you need to bleed the radiators. To bleed the radiators, you need a radiator key. Most boilers come with these keys. They are also readily available in DIY shops.

The first step is opening the release valves located either to the side or on top of the radiator. As you turn the radiator, you’ll notice air and water escaping. Because of this, you should have a bucket under the radiator to catch the water and sludge. You should also line rags around it to soak up stray water.

Once the pressure reduces to normal, you should close the valve. Because of the flowing water, this fix should be done when the boiler is turned off and has cooled down.

Casting faults

In boilers with cast iron exchangers, a fault in the casting can result in non-uniform heat transfer and consequently cause overheating. Heat exchangers in boilers transfer heat from the gas to the water.  The water is heated as it passes through the heat exchanger through a flow pipe. The water goes through the system and returns through a return pipe for reheating.

Casting faults are commonly caused by limescale build-up in the exchanger. But aside from the hotspots created, limescale build-up also causes the heat exchanger to crack and leak.

How to solve it?

To solve this problem, you should attend to the limescale build-up as outlined under limescale build-up. Though it can be fixed, it will cost you about £500. Because of the high repair costs, it’s wiser to spend the money on a new boiler.

Is it dangerous?

Overall, you don’t have to go into panic mode when you hear these noises. Boiler kettling is approximated to be only 13% urgent. However, though it is not a life a death situation, you should make a point of attending to it. Kettling usually points to serious boiler problems.

You can try and quiet the noise with the above quick fixes. However, if the noise persists, you should call a professional gas safe engineer to diagnose and fix the problem. And lastly, if your boiler is older than 10 years and the repair costs are more than £300, consider having a new boiler installed. It will save you money in the long run.

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