Our boiler is often an appliance that we take for granted. As long as it’s working, we don’t have to think about where our hot water comes from or how our radiators heat up. Generally, there is little to do in the way of maintenance, apart from the occasional pressure check and annual service.
However, as with any piece of equipment, things can and do go wrong from time to time - and an unfamiliar or unexpected noise is often the first sign. Such noises can occur even if everything seems to still be working properly, but a noisy boiler should never be ignored.
So, if your boiler is making unusual noises, what should you do?
The first step is to work out where the sound is coming from. Sometimes, noises can be misleading and may travel and echo through the heating system, therefore it is important to establish if it is a noisy boiler, radiator or central heating pipe, each of which can have different causes.
You should check your boiler for a fault code too, as this could help to explain the noise it’s making. Fault codes will show on the digital screen on the front of the boiler.
Below, we’ve identified some common boiler noises that could suggest there is a problem, including gurgling, vibrating, buzzing, banging or whistling. Use the descriptions to find out what kind of noise your boiler is making and how to fix it
Gurgling in a boiler is fairly common and is usually the water moving through the system, so it’s typically not a huge cause for concern. However, if the gurgling becomes constant or is loud enough to catch your attention, this could be a sign that something may need adjusting.
Gurgling can be caused by trapped air in the system, in which case bleeding your radiators could solve the problem, but it could also be down to low water pressure, lack of water in the header tank or a frozen condensate pipe.
There are many options when it comes to fixing a noisy, gurgling boiler but we have listed some of the most common below: bleed the radiators, check the water pressure, check the circulation pump and check the condensate pipe.
1. Bleed the radiators
In most cases, gurgling noises that may appear to originate in the boiler are actually caused by air elsewhere in the system. This is very common and can be easily remedied by bleeding the system. You can find our guide on how to bleed a radiator here.
If you’re unsure about completing this task yourself or encounter any difficulties, contact a professional heating engineer to finish the job for you.
2. Check the water pressure (and repressurise if necessary)
Low water pressure can cause gurgling and this can easily be checked using the pressure gauge on the heating system, this can be typically located on the boiler or in the airing cupboard. The gauge will likely have sections highlighted in red and in green. The needle within the dial should sit in the green section, which shows the pressure is just right. If it is in either of the red zones, the pressure is either too low, and more water needs to be put into the system, or too high, and some water needs to be let out.
Generally, a gurgling noise is caused by low pressure and so if the dial shows the pressure is below one bar, use the filling loop to add more water and recheck the pressure gauge. These might be a digital display format on newer boiler models that give you either a number or digital dial.
3. Check the condensate pipe
The condensate pipe is where excess water vapour can leave the system. When it’s very cold outside, the water can freeze, blocking the pipe. If your boiler is gurgling, check that this isn’t the case. If you do happen to notice icicles on the pipe, use warm water to gently melt them.
4. Check the circulation pump
Another you can check is the circulation pump. It can begin to make a noise when it’s running too fast and so there may be an option to slow it down. If you’re unsure of what you’re doing, a heating engineer will be able to resolve the problem for you. You’ll know if there is a problem with the pump because you’ll also likely find that you have no hot water and your radiators aren’t heating up properly.
If your boiler is whooshing and vibrating, which can also sometimes sound like humming, it could mean the following:
Pumps have a big part to play in your heating system, but they don’t always work as they should. A vibrating or humming sound could suggest that the pump is malfunctioning and moving around too much inside its casing or it could be that the pump is running too quickly. When the latter is true, the water that’s been heated by your boiler could move around the system too quickly, causing vibrating or whooshing noises.
Your boiler and heating system relies a lot on pressure, too. Low pressure can cause issues, as we’ve seen with gurgling noises, but so can high pressure. If the pressure in the system is too high, the valves inside your home can start to hum.
Finally, humming or vibrating could be caused by a blockage in the air intake or flue. As the flue is located outside, it’s not uncommon for it to become blocked with leaves, feathers and other debris. People have even found bird nests inside their flues in the past!
If you think that your boiler is vibrating, humming or whooshing, there are a few things you could check.
1. Check the pump
As with a gurgling boiler, you should check the pump to ensure that it’s not shaking or vibrating and that it’s set to the right speed. If the speed needs adjusting, you may need to call out a suitably qualified engineer to take a look for you. This might be the case if you have a combi or system boiler as the pump will be inside the sealed casing of the boiler.
2. Check the pressure
High pressure could be a culprit of humming or vibrating noises. Use the pressure gauge on the front of the boiler to check that the pressure is under 1.5 bar when the radiators are cold. If it isn’t, you may need to reduce the pressure by removing some of the water in the system. We have a guide on depressurising your system here. It's common for the pressure to rise when the radiators warm up, the pressure will typically rise from between 1 when cold to 2 bars when hot depending on the size of the system. If you get a rapid rise in pressure going up to 3 bar and over then a heating engineer is required as this would indicate a fault.
3. Check the air intake/flue
Blockages can occur in the air intake and this could be the cause of a vibrating or whooshing sound. The easiest way to determine this is by checking the external pipe on your property to make sure that there is nothing blocking it and remove any obstructions, such as foreign objects or fluff. If you place your hand near the vent, you should be able to detect a certain amount of air movement.
A buzzing or whining sound coming from inside your boiler is a genuine cause for concern that is typically caused by worn pump bearings, vibrating fan bearings or a defective burner. Unfortunately, these are all problems that should only be diagnosed and remedied by a qualified professional. Action should be taken sooner rather than later to prevent further damage.
Buzzing can sound quite similar to humming or vibrating, so we’d advise making the checks listed above under ‘How to fix a vibrating or whooshing boiler’. If those things seem okay, a buzzing boiler can be a sign of worn pump bearings, which may require a new pump altogether, vibrating fan bearings or a defective burner. All of these things should be looked at by a Gas Safe qualified engineer as soon as possible.
Because your boiler repeatedly heats up cold water, there’s a lot of expansion and contraction involved in the system, which can cause banging noises. However, this constant movement can cause issues, particularly with the pipework.
Over time, the pipes can come loose under the floorboards and move when the hot water flows through them. This can cause a banging noise that may echo and sound like it’s coming from your boiler.
Banging can also be caused by a boiler that’s overheating the water. Sometimes this can occur when limescale has built up on the heat exchanger or it could just be that your boiler is set to the wrong temperature. A faulty boiler thermostat can also disrupt the communication between itself and the boiler, causing the appliance to accidentally overheat.
As we’ve mentioned, a banging boiler can be caused by loose pipes, overheating or a faulty thermostat.
Where possible, pipes should be checked over and secured properly in place. Screws can come loose over time and must be retightened to keep the pipes from moving when the hot water travels through them. This job can be messy, as it means taking up carpets or flooring, so you may want to check the other potential fixes before resorting to doing this.
Another thing to check is the boiler temperature. Boiler set flow temperature should be set as low as practicable to satisfy the heat demand for the house on a combi, on a system boiler it should be set as low as practicable but not lower than the hot water tank set point unless on a 4 pipe system boiler or set up for priority domestic hot water (PDHW). The lower the boiler set flow temperature the more efficient the boiler will run. Use the boiler’s digital screen to find the temperature it’s set to and reduce it if needed. You shouldn’t set the hot water tank temperature below 60 °C as there’s a risk of contracting Legionnaires’ disease.
The final thing to check is your thermostat, as there can be a faulty connection that’s causing the boiler to misread the temperature you’ve set. A heating engineer should be able to test the system for you and make sure that the boiler thermostat is working correctly.
A boiler that’s whistling may be a sign of a limescale/rust buildup. Your heating system is constantly exposed to water, but when water and oxygen are combined with metal, rust can begin to form that can clog up pipes. For households in hard water areas, too, the water contains minerals like calcium and magnesium that can solidify into limescale and build up on pipes too. With all this debris and rust in the system, blockages can occur and the matter can even begin to get stuck in parts of the boiler.
This is when problems can start. If the boiler’s heat exchanger contains debris, the boiler can overheat and generate steam, a process called kettling. This is why it begins to make a whistling noise, much like a kettle when it comes to the boil. When kettling is left, the problem can get worse and your boiler may eventually break down altogether.
Whistling may be fixed by removing some of the air in the system, so try bleeding your radiators first to remove any excess air. If the noise continues, it is likely that kettling is the cause.
Sometimes, the debris can be removed from the system by flushing it. This involves taking out the old, rusty water and replacing it entirely with fresh. However, this doesn’t always get rid of the accumulation of limescale on the heat exchanger in the boiler. For more advice on fixing a kettling boiler, you should speak to a qualified engineer.
Hopefully, some of the noises and fixes we’ve mentioned should be enough to quieten your boiler. Remember that you should only perform routine maintenance on your boiler if the manual instructs or advises you to do so. These tasks always involve accessible areas and will never require the use of special tools to access any sealed parts of the equipment.
If you are not confident or have attempted to perform such tasks without success, then you should contact a Gas Safe registered engineer. You may also wish to check if the engineer is accredited or has been trained by your boiler manufacturer.
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