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Boiler Making Noise When Switched Off


Indeed, boilers aren’t the stealthiest appliances in the house. However, there are limits as far as noise is concerned. You should be worried if your boiler is making new noises that weren’t there during its installation.

“But my boiler is working fine. It can’t be that bad.”

Sure, your boiler might be working well despite the noises, but that doesn’t mean everything is fine. Some noises are a sign that something is wrong with your boiler. If you’re not careful, the problem might worsen with time. Your boiler might break down when you least expect it. Not only will it be inconvenient, but it can also be dangerous to your household members.

Of course, boilers can’t speak. They produce different noises, and each one of them has a meaning.

Reasons Why Boiler Making Noise When Switched Off

Banging noises

Boiler banging noises are perhaps the most common and frightening. Usually, they are caused by delayed ignition or kettling.

Delayed ignition is a common problem for traditional gas boilers that use pilot lights. Nowadays, modern gas boilers use electrical ignition systems that are more efficient and accurate.

When you start your gas boiler, the gas valve opens to allow gas into the combustion chamber. In an ideal situation, the pilot light will immediately light the gas to produce jet flames that will heat the heat exchanger.

However, if the pilot light delays, the released gas will accumulate in the combustion chamber. It will continue accumulating until it sets off a mini-explosion that produces a bang. This is a dangerous situation that can be hazardous. We advise you to call in an engineer immediately.

Kettling is a universal problem that affects almost all boilers. Basically, it’s caused by limescale build-up that creates bubble “hotspots”. When the bubbles pop, they produce banging noises. The best solution is a total system cleanup to remove the limescale buildup with the help of a dissolving solution. Once again, we advise you to call a professional who knows his way inside a boiler.

Whistling noises

In our opinion, whistling noises are the second most common. Usually, they are a sign of kettling, high boiler pressure, and even low boiler pressure.

Kettling. As mentioned above, it’s caused by limescale build-up. The solution is to clean the entire boiler system.

High boiler pressure. Sounds scary, doesn’t it? Well, it can permanently damage your boiler. Most of the time, the whistling noise is a result of trapped air trying to exit the system via small openings.

Before you jump to conclusions, take a look at your boiler’s pressure gauge. If the pressure is above 1.5 bar, then you’ll have to do something.

Boiler bleeding is the solution. As the name suggests, you bleed the boiler until its pressure is back to normal.

Don’t worry. At the end of this article, we have explained step-by-step how to bleed your boiler.

Low boiler pressure. Unknown to most people, low boiler pressure can also cause whistling noises. It happens when there isn’t enough water in the system. Therefore, when you turn on the heater, the little water starts boiling erratically.

Once again, we advise you to check your boiler’s pressure gauge and see if the pressure is below 1 bar. If that’s the case, then you’ll have to repressurise your boiler. Continue reading for more on boiler repressurising.

Gurgling noises

Gurgling noises are also caused by high boiler pressure and trapped air. As mentioned earlier, the best solution is to bleed your boiler down to the required pressure. Usually, that’s between 1 and 1.4 bar.

In case you didn’t know, hot air circulates between the radiator and boiler. As the years go by, some of the hot air tends to seep into the water pipes. Thus, bubbles are created. Those bubbles then mess with the boiler’s water distribution leading to a decrease in overall efficiency. If you don’t solve the problem early on, it might cost a lot in electricity bills.

Once you bleed the system, you’ll have removed the trapped air from the water pipes, and there will be good hot water circulation. It will improve heat distribution and restore the boiler’s efficiency.

How to bleed your boiler

You might have noticed that most of the problems we’ve mentioned are caused by high or low boiler pressure.

High boiler pressure is when the pressure gauge shows readings beyond 1.75 bar. If that’s the case, then you’ll have to bleed your boiler. High pressure can be dangerous since all that buildup pressure has to be released somehow.

  1. Of course, different boilers come with different structures. We advise you to have your user’s guide nearby for clarifications. First, you’ll have to locate your boiler’s bleeding valves. Generally, each radiator has one.
  2. To undo the valve, you’ll need your model’s radiator bleed key or a flat screwdriver. If your boiler was installed by a professional, then he should have left the key with you. Otherwise, your user’s guide should show you the key’s location.
  3. Turn on your boiler. This should cause air to rise to the top of the radiator. That way, it won’t interfere with the process.
  4. Before you open the radiator valve, we advise you to place a bucket or towel just under it.
  5. Open the radiator’s bleed valve, and you’ll notice some air escaping. At the same time, you should keep your eye on the pressure gauge.
  6. After a while, instead of air, you’ll see water escaping. It’s now time you closed the bleeding valve and moved to another radiator in your house (If there are others).

How to repressurise your boiler

Repressuring increases your boiler’s low pressure. You should also consider repressurising if you’ve “over-bled” your system.

  1. Before you begin, confirm that all bleed radiator valves are tightly closed.
  2. Next, you’ll need a boiler filling loop. Likewise, if your system was installed by a professional, he should have handed it to you. If that’s not the case, then you’ll have to buy one. They are relatively affordable. Nonetheless, we advise you to look for one that will work with your unit’s model. Take note that some boilers have internal filling loops. Confirm with your user’s guide to be sure.
  3. After attaching the filling loop to your boiler, open the filling valve as you monitor the pressure gauge. Ideally, you want your boiler to operate at a pressure of 1.5 bar.
  4. Once you’ve achieved the desired pressure, close the valve completely and detach it from the boiler.


Apart from being scary, boiler noises might hint that something is wrong with your system. Hopefully, we’ve given you some information to help you out. If all doesn’t work, then we advise you to call a gas engineer.

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