Boiler making noise when switched off

We have come across a lot of people complaining about their boiler making noise when switched off. You probably cannot count on boilers to be in the list of quietest heating appliances so far, but some sounds from your system can ensure you on the existence of a problem in your unit and that is when you need to learn on why your boiler is making noise when heating is on.

The boiler might be working properly right now, but it is likely to break down in the immediate future, and could be posing a serious risk to you and other people at the moment. And that is probably why you need to learn about your boiler making noise when switched off.

While you boiler might be producing different noises, each of them would carry different reasons and solutions. Let’s have a look.

  1. Banging Noise- A banging noise could either be a result of Delayed ignition or that of Kettling.
  2. The problem of delayed ignition is quite commonly found in gas boilers that use pilot lights in contrast to the electronic ignition systems. When a gas boiler receives the call for heat, the gas valve opens and releases a small amount of gas into a sealed combustion chamber through small “jets”. This gas then gets ignited by the pilot light and the jet flames heat up the heat exchanger. Delayed ignition occurs when the gas that is sent into the combustion chamber doesn’t immediately ignite. And when that happens, the gas builds and builds inside the combustion chamber until bang, creating a mini explosion.
  3. While on the other hand, kettling is something which occurs as a result of the lime scale buildup in the system that eventually creates bubbles and leads to the occurrence of ‘hot spots’.  These hot spots are what causes loud noise and needs to be treated with a solution in order to clear the lime scale blockage. However there are a number of other reasons as well that can cause kettling.
  4. Whistling Noise- There can be 3 main problems that happen to be the reasons of your system making a whistling noise.  
  5. Kettling is something which occurs as a result of the lime scale buildup in the system that eventually creates bubbles and leads to the occurrence of ‘hot spots’.  These hot spots are what causes loud noise and needs to be treated with a solution in order to clear the lime scale blockage.
  6. The other reason could probably be the air that gets trapped in your system and simply needs to be released out. While if the problem is that of the air being trapped then it can simply be repaired by releasing the trapped air from the system through the process of bleeding.
  7. However, this sound of whistling can also be a cause of the loss of water pressure or a blockage. It might be the case in which there isn’t enough water flowing through the system due to the low pressure. That is why your boiler is whistling when hot water is on. You need to look at the pressure gauge to check the pressure. If you find the pressure to be lower than one bar, then you would need to repressurise the system.
  8. Gurgling Noise- If you find your system pressure to be too high then releasing some of the air out of the system would likely solve the problem of the gurgling sound for you and put the pressure down to a required level.
  9. The hot water circulates between the radiator and the boiler through pipes. Over the time, the air seeps into the pipes, creating air bubbles which then interfere with the distribution of water in the pipe and the vessel, thus reducing the efficiency level of your system and generating huge energy waste which certainly increases your energy bills. 
  10. Bleeding the system would, therefore, allow a good circulation of hot water in the pipe lines, and would eventually result into uniform heat diffusion along with a cut down on your energy bills.

So following were the reasons of your boiler producing different sounds. While we have mentioned ways to bleed and repressurise your boiler, in any other case you are recommended to fall for a professional help in order to prevent any cause.

Bleeding you boiler system

  1. Depending on the type of bleed valve in your system, you need to undo it using a radiator bleed key or a flat screwdriver.
  2. Now put the boiler system off in order to allow the air to rise to the top of the radiator and prevent it from interfering during the process.
  3. Use a pair of grips to ensure that the valves at the bottom of your radiator are open in order to allow the water to flow into the radiator.
  4. Now loosen the radiator’s bleed valve with a radiator key or a flathead screwdriver.
  5. As soon as you loosen the bleed valve, you will be able to hear hissing sound of the air escaping.
  6. Once the water begins to come out, you know that all the air has been released from the radiator. Now tighten the bleed valve back.
  7. It is recommended to keep a cloth ready for any droplets that would come out of the system as soon as the air escapes.
  8. Now go around each of the radiators in the house, repeating the process if required.

Re-pressurizing your system

  1. Close all the vents

Before getting start with re pressurizing your boiler, check all the bleed valves on radiators and towel rails to be fully closed.

  • Search for the filling loop

In most of the boilers, they have the external filling loop that is used to top up the boiler with water and hence increases the pressure.

  • Open the filling loop

As soon as you open the filling loop, you will get to see a pressure rise. You can take a look of what is the exact pressure your boiler needs. Commonly the boilers operate with 1.5 bars.

  • Close the filling loop

Make sure that the filling loop is completely closed. However if it is not closed it will slowly leak additional water into the boiler. This will increase the pressure and the boiler will lockout.

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