For the vast majority of the time, our boiler is something that we take for granted. As long as it keeps on working properly and we have a constant supply of hot water and heat as required, there is little to be done in the way of maintenance, apart from the annual check. 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. For many people, they can be very worrying. Even the smallest of noises can also cause problems such as frustration and sleeplessness, which adds to the stress.

So what are the common reasons why your boiler is making a noise and what can you do to solve the problem? Let’s take a closer look.

Sounds can sometimes be misleading, especially inside houses. The first step when faced with a noise in the system is to identify exactly where the sound is coming from. Because sounds can travel and echo through the heating and water system, it is important to first establish if it is actually a noisy boiler, or a noisy radiator or central heating pipe, each of which can have different causes.

If you are happy that the noise is coming from the boiler, then the following steps will help you.

Many modern boilers now come with digital displays which include error codes. Before spending time to diagnose problems yourself, familiarise yourself with the product manual as this could save valuable time.

If you don’t have the original manual, an online search with the make and model number can often find an online version. For Viessmann boilers, most possible fault codes can be found on our dedicated fault code identifier page. However, be aware that not all problems will generate an error code so the following steps may still be necessary.

A small amount of gurgling within a boiler is fairly common and is no cause for significant concern. However, if the gurgling becomes constant or is loud enough to catch your attention, this is a sign that something may need adjusting. In some cases, a gurgling sound may be mistaken for the sound of water boiling within – this is unlikely to be the case so don’t panic. Take the following steps to diagnose and eliminate the problem, if you are confident to do so:

1. Bleed the system

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. There is no need to get an expert involved, all you need to do is follow a few simple steps:

1. Fully open all radiator thermostats and run the heating at full temperature for 10-15 minutes with all radiators on
2. Turn the circulation pump off and wait until radiators are cool – usually 30-60 minutes
3. Bleed the radiator nearest the boiler using a bleed key or screwdriver until water comes out
4. Repeat this for each radiator
5. Turn on the boiler and check the water pressure (see below).

If you are unsure about bleeding the system or encounter difficulties at any point, it is advisable to contact a professional at the earliest instance.

2. Check the water pressure

If the water pressure is too low, this may be the culprit of your gurgling noises. Your boiler will have a pressure gauge, also known as a manometer, located in the area where the pipes are connected to the boiler itself. Most modern pressure gauges will be marked with the correct pressure level, although you may need to consult the manual. If it is too low, then increase the pressure until it is restored to the correct level. This may require a topping up of the water level.

3. Check the circulation pump

If the noises continue after you have taken the previous actions, there is a possibility that the problem may lie in the circulation pump. In most cases, the noise will be caused by this pump operating at an excessive speed. If the boiler has an option to slow it down, this may solve the problem. It may, however, be necessary to have a trained engineer perform this task.

A boiler that begins to make loud ‘whooshing’ noises and vibrate excessively can be very scary, however the actual cause may be quite simple to diagnose and fix. Whilst there is no immediate danger, allowing the problem to persist can cause further damage so immediate action should be taken.

1. Check the air intake/flue

The most frequent cause of a loud whooshing sound is a blockage to the air intake. Check the external pipe on your building to make sure that there is nothing blocking it and remove any obstructions such as foreign objects or fluff. If you place your hand over the vent, you should be able to detect a certain amount of air movement.

2. Check the air filter

A blocked air filter is now one of the most common causes of boiler problems. The air filter in a boiler is not unlike the filters you will find in a vacuum cleaner or car. If the air filter is user-serviceable, remove it and clear it of any dirt build up with a vacuum cleaner or dry brush. It may be necessary to engage the services of a professional for this step.

A buzzing or whining sound coming from inside your boiler is a genuine cause for concern that is typically caused by worn pump bearings, a defective burner or vibrating fans. 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.

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.

When it comes to choosing a new or replacement gas boiler, it is easy to become confused by the many different types of boiler available. For those less familiar with some of the terms in use, it is easy to find yourself asking if there is a difference between a combi boiler and a condensing boiler? 

Read on to discover everything you need to know about gas condensing boilers including how they work and what to look out for.

It is important to understand the difference between these two words which can be easily confused. To help understand the difference, let’s take a closer look at what they mean.

The term combi boiler is short for combination boiler and refers to a boiler that is able to provide both heating and hot water within a single unit. They are supplied by mains water, which is heated internally.

Unlike an immersion heater, a combi boiler heats your water on demand, instead of storing it in a tank. This means there is no need to have a separate header tank or storage tank for hot water as was commonly found in older houses.

As well as saving space, combi boilers are generally considered to be the most economical type of boiler in the domestic environment and the best choice for the majority of households.

A condensing boiler is any boiler which uses condensing technology to make better use of the heat they generate from burning fuels such as gas or oil – so a combi boiler can also be a condensing boiler.

Older, non-condensing boilers wasted between 30-50% of heat due to combustion gasses escaping into the flue. Thanks to modern technology, a condensing combi boiler, in contrast, can be up to 99% efficient. So how is this possible?

In a condensing boiler, heat existing in the flue gasses can be captured and ‘recycled’ back into the heating system and used to preheat the cold water entering the boiler. During this process, the temperature of the flue gas is rapidly reduced from around 130℃ to 50℃.

Because they are able to reuse energy that already exists, condensing combi boilers help to save money on your energy bills. They also have a much lower carbon footprint, helping you to combat climate change by reducing CO2 emissions.

Non-condensing boilers generally take in air from inside the room. A condensing boiler, on the other hand, captures air directly from the outside of the room it is placed in and is completely sealed for heat insulation.

This means that there is no risk of anything being sucked into the boiler.

Another safety advantage is that because the condensed liquid is disposed of via a pipe connected to the drainage system, there is no risk of being in contact with toxic substances.

Advances in technology mean that modern boilers are incredibly reliable. However, because every type of boiler is different, they all have certain advantages and disadvantages.

As mentioned in the previous section, a condensing boiler produces a constant flow of condensate which drains into your household’s waste water just like your sink and washing machine.

For safety, if the outlet becomes blocked your condensing boiler will automatically stop. The most common cause for this is a frozen boiler condensate pipe.

This is most likely to happen if your boiler has been fitted with a condensate pipe that is outside the building and therefore exposed to lower temperatures. Although a relatively common problem during cold snaps, it is easily prevented and fixed.

There are two key factors to consider when deciding what size of condensing gas combi boiler to buy – how much hot water you are likely to use and how many rooms you will need to heat. For most standard 2-3 bedroom houses with a single bath and shower, a combi-boiler of between 24-30 kW is a good choice.

For homes with an additional en-suite bathroom or more rooms, a larger 30-35 kW boiler would be recommended.