14 August 2020
Top seven common causes of boiler breakdowns

Top seven common causes of boiler breakdowns

We detail some reasons why your boiler might develop a problem, what caused them, and what you can do to prevent them from happening.

Modern boilers are generally built to last. But, just like any other appliance or system in your home, they’re not perfect, and sometimes things can go wrong.

This article will help you identify issues with your boiler, especially if you’re experiencing any of the following symptoms:

  • My boiler is switching off
  • My boiler locks out regularly
  • My boiler has a leak
  • My boiler is making a new noise
  • My boiler is louder than usual
  • My water is not hot
  • My heating won’t come on
  • I can’t top up my boiler’s pressure
  • I need to top up my boiler’s pressure regularly
  • My boiler’s pressure is too high

Here are the most common causes of boiler breakdowns and how to prevent them from happening:

#1 Cause: Lack of regular servicing

Just like a car, regular services for a boiler are essential if you want to spend less money on repairs and maximise its lifespan.

The average lifespan of a modern boiler is around 10 to 15 years (depending on the make and model, the availability of parts, and other factors). Each time a service is missed or a repair is put off, this lifespan decreases, and the chance of a boiler breakdown increases. This can cost you more in the end.

For a small yearly cost, an annual service can increase the lifespan of your boiler and help you avoid boiler breakdowns. It also means you can relax, knowing your boiler is heating your home and hot water efficiently.

#2 Cause: Old age

Your boiler’s components go through severe thermal and mechanical stress. This eventually results in mechanical failure or troublesome leaks. Over time rust and corrosion build up and spread, causing deterioration. Debris and dirt can also accumulate and restrict water flow or prevent the mechanics of your boiler from working efficiently.

You may be able to spot some corrosion on the visible parts of your boiler, but it usually required a more detailed inspection under the cover. If your boiler is over ten years old, ask an engineer to assess its current condition and potential longevity.

Get a free quote for a replacement boiler.

#3 Cause: Leaking

Boiler leaks

A boiler leak is typically due to an issue with an internal component, like a pressure valve, pump seal, or heat exchanger:

  • Pressure valve: An issue with this component can cause your boiler’s pressure to rise so high that it results in a leak
  • Pump seal: Natural wear and tear of your boiler’s pump seal can cause leaks – it will need to be replaced
  • Heat exchanger: Corrosion around your boiler’s heat exchanger can also cause leaks, although this is more unusual – this is the worst-case scenario in terms of leaks and almost always leads to a boiler replacement

Leaking pipes

The most common type of leak that can cause you problems is leaking water pipes, typically those pipes under your boiler. Over time, water gradually combines with the metallic debris within your system to corrode the copper piping. This leads to small gaps through which the water escapes.

If your boiler is new and you can see water leaking from the pipes underneath it, there may be some joints in the pipework that haven’t been fitted correctly. This is surprisingly common and easy to put right. Ask your original installer to return or contact us for assistance.

Boiler codes for leaks

Your boiler may be able to detect leaks and provide you with a clue in the form of an error code. These codes vary between manufacturers, but here are a few examples:

Baxi boiler leaking water
Common error codes: 117, 118, 125, E78, H.02 – 06

Worcester Bosch boiler leaking water
Common error codes: A1, E9, CE207, HO7

What to do

Check your boiler and pipes regularly for obvious signs of leakage, especially during the winter months. Contact our team of expert boiler engineers to assess and fix any leaks (for your own safety, please don’t attempt to address any boiler issues yourself).

#4 Cause: High pressure

Boilers don’t deal well with too much pressure. If your boiler's pressure is too high, the PRV (pressure release valve) will discharge the excess water, or parts will fail, causing a leak.

The pressure gauge on your combi or system boiler should be between 1 bar and 1.5 bars, within the green markings. Anything above that green bar indicates that your boiler is over-pressurised.

There are several causes of high pressure. The first thing to check is your filling loop tap. This is usually located underneath your boiler. It should be firmly closed. If you have recently topped up your boiler pressure, this will be a likely cause.

Your heating system may need to be bled. Bleeding your radiators is something you can tackle yourself if you have a radiator bleed key, some time, and a bit of confidence. We’re happy to help if you want to leave it in the hands of heating system experts – just get in touch.

#5 Cause: Low pressure

The opposite to high pressure, low water levels can cause your boiler to shut down completely, leaving you without heating and hot water. It shuts down to prevent overheating that would damage components.

You can often rectify this issue yourself by topping up the pressure. This can be done safely using the filling loop tap, normally located underneath your boiler. Top up the pressure so it’s within the ‘safe zone’ marked in green – between 1 bar and 1.5 bars of pressure. Ensure the tap is firmly closed after topping up.

If you find yourself topping up the pressure regularly (for example, more than a few times a year), this could be a sign of an underlying issue. A component might be damaged, or, if you have a modern combi boiler, your expansion vessel may need to be recharged.

If you have recently bled your radiators, you will need to top up the pressure again.

Low boiler pressure can also be caused by:

  • a system leak
  • a failed component like a value or diaphragm
  • a failed seal
  • a faulty thermostat

You can look for a leak under your boiler but may need to contact a Gas Safe engineer to remove the casing of your boiler and perform a thorough inspection.

#6 Cause: Dirty water and sludge within your heating system

Many boiler breakdowns are caused by dirty water and sludge within the heating system. When this builds up, it can have a considerable effect on how well your boiler runs and how efficiently it performs.

Cleansing and powerflushing will improve your central heating system, help you use less energy and keep your home warm. We recommend a powerflush for your system every five years.

#7 Cause: Stress due to heat loss

Heat loss is a calculation that measures the heat your house loses on the coldest day of the year. The heat loss of your home takes into account things like:

  • The total floor area
  • The number of radiators
  • The number of doors and windows in your property
  • How well your doors and windows prevent drafts
  • The quality and effectiveness of your insulation

These are all factors that directly affect how well your heating system can perform. For example, poor insulation will mean your boiler will have to work harder to maintain the temperature you program through your heating controls. The harder a boiler has to work, the more stress on its components. This can lead to issues.

Other potential causes

Heating systems are complicated beasts, and there are other less-common boiler breakdown causes we haven’t listed here, including:

  • A frozen condensate pipe during the winter
  • Your boiler failing to respond to your thermostat
  • A build-up of limescale
  • A faulty pump
  • Air in the system
  • Pilot light switching off (applicable to mainly older boilers)
  • Boiler not switching on due to lack of power

Problem with your boiler? We’re here to help

Our experienced heating engineers can perform assessments of your heating system to identify any potential problems. It’s best to get any minor issues checked out before they can develop into more significant problems.

If you still need some advice, call our friendly team on 0800 3899 463 (Mon to Fri, 9am to 5pm) for help, or use our online enquiry form.

We provide oil and gas boiler servicing and heating system repairs right across the East Coast of Scotland.


Written by Kingdom Gas Services team