9 Signs Your Boiler Needs Servicing

Is your boiler making strange noises or not heating your home as efficiently as it used to? If so, it might be time for a service.

In the UK, where reliable heating is crucial given the unreliability of the weather throughout the seasons, keeping your boiler in top condition is essential. What’s more, regular boiler servicing can prevent a large majority of breakdowns, saving you from unexpected and potentially costly repairs should the worst happen.

Broken and leaking gas combi boiler and connecting pipe work view from underneath

Consider the story of Jane from Stockport. Last autumn, her boiler started making an unusual banging noise. She ignored it initially, only to find herself without heating during a particularly frosty November. A quick call to our heating engineers revealed that a simple service could have prevented the issue, saving her both time, money, and considerable stress!

Boilers, much like cars and any other machines, need regular check-ups to make sure they run properly. But for many of us living busy lives, the health of our boiler doesn’t fall too high on the priority list, especially during summer.

The fact is though, without regular servicing, your boiler could break down unexpectedly (and usually at the worst time), leaving you in the cold and facing high repair costs.

To help you avoid this, in this article, we’ll identify the key signs that your boiler needs servicing, from odd noises and fluctuating temperatures to steadily rising energy bills. Read on to learn how to keep your boiler in top shape.

9 signs your boiler needs servicing

Unusual noises

Unusual noises are often the first sign of a deeper issue within a boiler system. They can indicate that the boiler is operating inefficiently, or indicate potentially dangerous issues like leaks or pressure problems.

Types of noises you might hear include:

Banging or knocking

Banging or knocking noises from a boiler are often caused by a phenomenon known as “kettling,” which happens when there is buildup of limescale on the heat exchanger. This buildup can restrict water flow, causing it to overheat and produce steam bubbles that make a loud banging noise as they collapse.

These noises can also be due to trapped air in the system or issues with the pipework expanding and contracting as it heats and cools.


Clunking sounds may be evidence of a faulty pump or problem with the fan inside the boiler. They can also be cause by blockages in the system or loose components, suggesting that the boiler needs immediate attention to prevent further damage.

Whistling or hissing

When air gets trapped in the pipes or radiators, it can create a whistling sound as water flows past the air pockets. Alternatively, hissing might indicate a leak or a pressure issue in the boiler. Leaks in particular can cause water to escape and, if the boiler is losing pressure, it can produce a hissing noise as air and water are forced through the narrow gaps.

Inconsistent heating and hot water

Some common symptoms of a boiler needing servicing include:

  • Uneven heating in different rooms
  • Radiators that take a long time to heat up
  • Lack of hot water or hot water take a long time to reach the desired temperature.

These sorts of issues can be caused by airlocks that stop hot water from circulating effectively, sludge buildup that blocks the flow of water, or failing components such as the pump of heat exchanger.

Leaks and water stains

The most straightforward sign of a leaking boiler is visible water around the unit. But you might also notice damp patches near the boiler or rust on the boiler, particularly near the joints and seams.

Common issues that cause leaks include corroded pipes (especially in older boilers), damaged seals that lead to water seeping out from the boiler, and faulty pressure valves.

Changes in pilot light colour

The pilot light in a gas boiler should burn a bright blue flame. If you notice that the pilot light is yellow or orange it could suggest incomplete combustion due to dirt in the burner, a faulty gas valve, or insufficient oxygen supply.

If the pilot light keeps going out, it could be because of a draft in the room, a faulty thermocouple, or issues with the gas supply.The thermocouple is a safety device that shuts off the gas supply if the pilot light goes out. If this is faulty, it might incorrectly shut off the gas even when the pilot light is functioning properly.

Another cause could be a blockage in the pilot tube, which can restrict the flow of gas to the pilot light, causing it to go out.

Increased energy bills

A sudden and unexplained increase in your energy bills is often one of the first signs that your boiler may not be operating as efficiently as it should, particularly if they can’t be explained by changes in energy prices, increased usage, or seasonal variations.

If you notice that your energy bills spike during periods when the boiler is heavily used, it’s a good sign it needs servicing. Over time, wear and tear can affect boiler efficiency as components like the heat exchanger, burner, and pump may degrade which means the boiler has to work harder and use more energy.

Low boiler pressure

A healthy boiler pressure is between 1 and 2 bars when the system is cold. If the gauge consistently reads below this range, it indicates low pressure.

Low boiler pressure is most commonly caused by leaks in various parts of the boiler system. Sometimes, these leaks aren’t easily visible. In such cases, you might notice a gradual drop in pressure without any obvious signs of water around the boiler or pipe joints.

Other common causes of low boiler pressure include:

  • Faulty pressure relief valves
  • Bleeding the radiators
  • Problems with the expansion vessel

Strange smells

Strange smells around your boiler are clear indicators that something is wrong and shouldn’t be ignored.

A metallic smell around your boiler can be a sign that parts inside the boiler are getting too hot or starting to fail.

A sulphur or rotten egg smell is a strong indication of a gas leak. If you notice this smell, it is important to act quickly by turning off the gas supply, ventilating the area, and calling a qualified gas engineer.

Visible soot or rust

The presence of soot around the boiler or on the heat exchanger is a clear sign of incomplete combustion, which happens when the fuel does not burn fully because of insufficient oxygen supply, dirty burners, or improper fuel-to-air rations. Soot appears as a black, powdery residue and is commonly found inside the boiler, around the burner, and on the flue pipes.

Rust on or around the boiler indicates the presence of moisture because of leaks or condensation caused by improper venting. Rust is particularly problematic because it not only indicates existing damage but can also cause further deterioration if not addressed quickly.

Boiler age and (lack of) maintenance

Older boilers are typically less efficient and are at increased risk of breakdown as, over time, the components can wear out.

If your boiler is old or hasn’t been serviced in a while, it’s important to get it checked for signs of wear and tear, leaks, or inefficient combustion. Servicing usually includes checking and cleaning the burner, inspecting the heat exchanger, ensuring proper ventilation, and testing safety devices like the pressure relief valve and carbon monoxide detector.

Without a doubt, preventative maintenance can help identify issues before they become a major problem, especially with older boilers. That being said, if your boiler is more than 15 years old, it may be time to consider a replacement so you can enjoy the efficiency improvements, reliability, and safety upgrades offered by modern boilers.

Why is regular boiler servicing so important?


One of the primary (and arguably most important) reasons for regular boiler servicing is safety. A boiler that is not serviced regularly can develop faults that may lead to dangerous situations, like gas leaks or carbon monoxide poisoning which can be fatal.

During a service, an engineer checks for leaks and makes sure that the boiler is burning fuel safely.


Over time, boilers become less efficient due to wear and tear, the buildup of sludge and debris, and other factors.

The main problem with an inefficient boiler is that it has to use more fuel to produce the same amount of heat, leading to (you guessed it) higher energy bills.

Regular servicing includes cleaning and tuning the boiler, which helps it run more efficiently, thereby saving you money on your heating costs. Winner!


Boilers can be a substantial investment, so of course you want to make sure they last as long as possible. Regular maintenance and servicing can help you do this and extend the lifespan of your boiler.

During a service, engineers can identify and fix minor issues that, if left unchecked, could lead to more significant problems or complete boiler failure.

How often should I service my boiler?

In the UK, it’s recommended that domestic boilers are serviced at least once a year.

While this isn’t a legal requirement (unless you’re a landlord, in which case you are legally required to carry out annual servicing and get a Gas Safety Certificate from a Gas Safe registered engineer), many manufacturer’s warranties for boilers only stay valid if the boiler is serviced annually by a qualified professional.

Furthermore, some home insurance policies may require proof of regular boiler servicing to ensure coverage in the event of a claim related to the boiler.

What are the dangers of not servicing a boiler regularly?

Neglecting to service your boiler regularly, especially if you spot any of the above signs, can lead to:

  1. Carbon monoxide poisoning
  2. Increased risk of breakdowns and costly repairs
  3. Reduced efficiency and higher energy bills
  4. Safety hazards from leaks and pressure problems
  5. Shortened lifespan of the boiler

In short, not servicing your boiler can lead to serious safety risks, increased costs, reduced efficiency, and a world of headaches!


Regular boiler servicing is important to ensure the safety, efficiency, and longevity of your heating system. Being able to spot the signs that your boiler needs servicing can prevent minor issues from developing into major, costly problems. So, be sure to look out for:

  • Unusual noises
  • Uneven heating
  • Slow to heat radiators
  • Insufficient hot water
  • Leaks and water stains
  • Pilot light issues
  • Increased energy bills
  • Low boiler pressure
  • Strange smells
  • Soot or rust.

If you notice any signs indicating your boiler needs servicing, contact a qualified heating engineer as soon as possible. Or, if your boiler continually loses pressure or breakdown, it may even be time to consider investing in a new one.

If you’re looking for boiler servicing or repair in Stockport, Manchester, and the surrounding areas, our Gas Safe and OFTEC Registered gas engineers are on on hand to help.

Contact us today for a free, no-obligation estimate and book your boiler service.

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