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What happens during a boiler service?

Booking your annual boiler service is one of those chores that can be tempting to put off, particularly if your boiler seems to be working fine. But regular servicing is vital in ensuring that your boiler stays safe and continues to run smoothly and efficiently for you. If you’re thinking about booking your service, you might be wondering what’s involved that makes it so important. So, we’ve put together a list of checks that your engineer will take when conducting your boiler service, so that you know what to expect on the day, and why you should be booking in for that service!

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An engineer conducting a boiler service.What happens during a boiler service?

Booking your annual boiler service is one of those chores that can be tempting to put off, particularly if your boiler seems to be working fine.

But regular servicing is vital in ensuring that your boiler stays safe and continues to run smoothly and efficiently for you. 

If you’re thinking about booking your service, you might be wondering what’s involved that makes it so important.

So, we’ve put together a list of checks that your engineer will take when conducting your boiler service, so that you know what to expect on the day.

We also explain why regular servicing is vital, whatever the age and condition of your boiler.

Who should conduct a boiler service?

Before we walk you through what happens during a boiler service, we want to stress that you should only ever use a Gas Safe registered engineer to work on your boiler. 

Only Gas Safe engineers can legally fit, fix, and service gas appliances.

Gas Safe engineers are authorised and regulated by the Gas Safe register. You can ask to check that your engineer is qualified to work on gas, by asking to see their Gas Safe ID card.

To find out why choosing a Gas Safe engineer is so important, you might like to read our related blog here.

Rest assured that our engineers at The Heating People are Gas Safe registered, and all of our work conforms to the highest standards.

What happens during a boiler service?

Now let’s look at what to expect when The Heating People service your boiler.

Just be aware that not all tests or checks will be applicable, it will depend on the type of heating system that you have:

Arrival of your Gas Safe engineer

An engineer advising customers.When one of our expert engineers arrives at your home, they’ll introduce themselves, and check that you were expecting the service.

Before they start, they’ll ask you a few quick questions about how your heating system’s been working recently, and whether you’ve noticed any issues with your boiler.

If your boiler has displayed any fault codes, or has done anything out of the ordinary lately, you should let your engineer know.

Your engineer will then prepare the area and protect your home by putting protective sheeting down, to keep your surfaces clear of any dust and debris.

Then the checks and tests can begin…

Check ventilation requirements

Your engineer will check that any ventilation requirements for the boiler have been met. Although the boiler itself doesn’t require ventilation, the waste gases produced by the boiler need somewhere to go. Your engineer will check that this is safe.

Visual Inspection of boiler and flue

Your engineer will visually check your boiler for any obvious safety defects.

This will involve inspecting your boiler controls to make sure that they are working correctly. Your engineer will look for any corrosion or leaks and will visually check the flame in your boiler.

Removal of the boiler casing

Your engineer will remove the boiler casing will and visually inspect the boiler, internally and externally, for any signs of distress.

Your engineer will check the functioning of the main component parts, such as the burner; heat exchanger; main injector; and spark/sensor probe.

Flue check

Your boiler’s flue is a pipe that carries exhaust gases produced by your boiler outside of your home and releases them into the atmosphere.

It’s very important that this is working properly, so that dangerous gases are not present inside your home. To check this, your engineer will conduct a flue test.

A flue test checks that the flue isn’t obstructed in any way and the flue components are sealed correctly to make sure that there are no unsafe emissions being released. 

Gas checks

Your engineer will conduct a gas pressure check to ensure that your boiler is operating at the right gas pressure. The gas valve will be adjusted to check the burner is combusing efficiently and correctly (using a flue gas analyser). A gas tightness test will be conducted to ensure there are no leaks.

Combustion analysis

Your engineer will use a flue gas analyser to test the products of combustion. This ensures that there are not high levels of carbon monoxide and to make sure the boiler is burning as the manufacturer intended it to.


Your engineer will clean the condensate trap, and if the other tests have indicated that it’s needed, the burner; heat exchanger; electrodes; and magnetic system filter; will also be cleaned.

Check the expansion vessel

Your engineer will check your boiler’s expansion vessel to ensure that it still has water pressure to the manufacturer’s requirements. Your engineer will top this up if needed.

Where safety problems are found

If your engineer discovers any safety defect(s) with your boiler, they will explain this to you, and will either fix them, or act in accordance with the Gas Industry Unsafe Situations Procedure (GIUSP).

If your engineer can’t rectify a safety defect, they’ll discuss with you any remedial action that needs to be taken, and will explain the options to correct the fault(s).

You might like to read our related blog: Condemned boiler? What to do next.


Your engineer will complete the Benchmark service record in your boiler’s manual, which is important to maintain your boiler’s guarantee.

If you’re a landlord, you’ll be provided with a Landlord Gas Safety Record to provide to your tenants, as required by law.

Why is it important to have my boiler serviced every year?

Unfortunately, many people overlook the importance of regular boiler servicing.

A survey by the Gas Safe Register found that a worrying 24% of homeowners have either never had their boiler serviced or haven’t had it serviced once a year as recommended. This is a worrying statistic!

Here are the reasons why you should have your boiler serviced annually, regardless of its age:

Regular servicing keeps you and your family safe

One of the most important reasons to have your boiler serviced regularly, is to keep you and your family safe.

After all, your boiler is a gas burning appliance, and we all know that gas can be dangerous.

Boilers have built in safety features to keep us safe. But if you neglect your boiler, faults can develop, leaving your boiler in an unsafe condition.

Unsafe gas appliances pose risk of fires and explosions, as well as carbon monoxide poisoning.

According to the NHS, around 4000 people are reported to go to A&E each year because of carbon monoxide poisoning, and sadly, 60 people will lose their lives.

Regular servicing ensures that your boiler is combusting fuel safely and efficiently, and any small faults can be fixed before they develop into anything potentially life threatening.

Regular servicing prevents problems from arising 

We all know that prevention is better than cure – and servicing your boiler is important for this reason.

You wouldn’t dream of driving a car without having a valid MOT, so it shouldn’t be surprising that something as hard-working as your boiler also requires some upkeep.

Servicing your boiler is a preventative measure to make sure it stays in good working order.

Your engineer will check, clean, and maintain your boiler to keep it running smoothly, and reduce the chances of it breaking down.

And whilst nobody wants to spend money on a boiler service, a service is much cheaper than a big repair bill or having to replace your neglected boiler!

Regular servicing will catch boiler problems early

Related to our point above, regular servicing allows your engineer to catch small problems before they turn into serious faults.

Problems only get worse the longer you leave them, and this could result in your boiler breaking down altogether.

A boiler breakdown is not only inconvenient, but typically more expensive to put right. And if you’ve neglected your boiler too long, it could be a complete write-off, and you’ll need a boiler replacement.

So, addressing boiler problems early will save you the hassle of a full breakdown, and money on future repairs.

Regular servicing maintains boiler efficiency and keeps your bills low

A family putting money into a piggy bank next to green shoots.If you’ve read our blog about boiler efficiency, you’ll know that an efficient boiler can help you to save money on your energy bills.

And the good news is, regular boiler servicing helps to maintain your boiler’s efficiency, thereby keeping your energy bills as low as possible.

But how does a boiler service help with boiler efficiency?

Well, over time, dirt and debris will build up in your boiler, preventing it from working at its maximum performance.

During a boiler service, your engineer will clear the internal combustion areas from dirt and debris, thereby improving the heat transfer. This allows your boiler to light more easily and burn efficiently, which can lead to lower heating bills. 

By having your boiler serviced regularly, you’ll be ensuring that your boiler is working to the best of its ability.

Regular servicing extends the lifespan of your boiler

A boiler is a big investment, and you’ll want it to be keeping you and your family warm and comfortable for as long as possible.

Looking after your boiler with regular servicing will help your boiler to run smoothly and efficiently, and will help to extend its lifespan.

With careful maintenance and regular servicing, your boiler will be able to work hard for you for 10-15 years or even beyond!

Regular servicing maintains your boiler’s guarantee

A viessmann boiler with a 10 year guarantee badge.Another important reason to have your boiler serviced every year is to maintain its guarantee.

We can supply guarantees of up to 14 years with our boilers. This gives you the peace of mind that should any faults develop within that time, they will be repaired free of charge.

But this will only remain valid as long as you keep up to date with regular servicing.


Regular servicing is a legal requirement for landlords

If you’re a landlord, a qualified Gas Safe registered engineer must, by law, check your gas appliances and flues annually to ensure that your property is safe for tenants to live in.

As a landlord, you’ll be required to present a gas safety record each year.

When should I get my boiler serviced?

Now that you know why it’s so important to keep up with regular servicing, you might be wondering when’s the best time to have it done.

The Heating and Hotwater Industry Council (HHIC) recommends booking your boiler service during the summer. This is to avoid any nasty surprises when the weather turns colder, and you need your boiler the most.

How long does a boiler service take?

A boiler service usually takes less than an hour, but this depends on what sort of appliance you have, and what condition it’s in.

Final thoughts…

A warm cat relaxing next to a radiator.We hope that you’ve found this article useful in understanding what’s involved in a boiler service, and why regular servicing is so important.

As well as keeping your boiler safe, maintaining your boiler will almost certainly save you money in the long run. Not just on your energy bills, but also in avoiding the cost of repairing or replacing a neglected boiler.

So spare a thought for the most hard-working appliance in your home, and probably the one you rely on the most, and book in for that service!

Check out our realted blog: 5 Benefits of your annual service.

Useful links:

HHIC: When to get your boiler serviced

HHIC: Consumer guide to boiler servicing

The Gas Safe Register