Annual Boiler Service Guide: What's Included and Why It Matters

What actually happens during a boiler service

A boiler service is a thorough visual and functional inspection carried out by a Gas Safe registered engineer, designed to confirm the boiler is running safely and efficiently. It is not the same as a repair visit; the engineer is not there to fix a known fault but to check the boiler over and catch anything that might become a problem.

The engineer will typically check the case and casing seals are intact, inspect the burner and heat exchanger, check the flue for correct operation and safe termination, test the gas pressure and burner pressure against the manufacturer's specification, and check the flame picture to ensure combustion is clean and complete.

They will also check the condensate pipe for correct fall and no blockages, test all the boiler's safety devices, check the pressure relief valve and expansion vessel, and inspect for any signs of leaks, corrosion or scale build-up around the boiler and associated pipework.

Why servicing matters for safety

The most important reason to service a boiler is safety. A poorly maintained boiler can develop a cracked heat exchanger or a blocked flue, both of which can lead to carbon monoxide escaping into the home rather than being safely vented outside. Carbon monoxide is colourless and odourless, which is exactly why an annual check by a qualified engineer, alongside a working carbon monoxide alarm, is so important.

Beyond the immediate safety benefit, a service also protects the long-term reliability of the boiler. Small issues such as a build-up of scale, a slightly worn seal, or a component starting to wear can often be spotted and addressed before they cause a full breakdown, which is both cheaper and far less disruptive than dealing with no heating in the middle of winter.

Servicing and your boiler warranty

Most manufacturers, including Viessmann and Grant, require an annual service by a Gas Safe registered engineer as a condition of keeping a longer warranty valid, particularly the extended warranties of up to 10 years available on some models. Missing even a single year's service can be enough for a manufacturer to reject a warranty claim, which can be a costly mistake if a major component then fails.

It is worth keeping a simple record of your service history, including the date, the engineer's Gas Safe registration number, and any paperwork issued. This is not just useful for warranty claims, it is also something buyers and their surveyors will often ask about if you come to sell the property.

Landlord gas safety duties

If you are a landlord in Harpenden, St Albans or anywhere else in England and Wales, you have a legal duty under the Gas Safety (Installation and Use) Regulations 1998 to have every gas appliance, flue and installation pipework in a rented property checked annually by a Gas Safe registered engineer.

You must keep a record of the safety check, known as a Landlord Gas Safety Record or CP12, and provide a copy to existing tenants within 28 days of the check, or to new tenants before they move in. Failing to arrange this check, or failing to provide the record, is a serious legal breach with significant consequences.

Many landlords choose to combine the annual gas safety check with a full boiler service, since an engineer is already on site and it makes sense to have both jobs done in a single visit, minimising disruption for the tenant.

How long a service takes and how often you need one

For a straightforward domestic boiler, a service typically takes somewhere between 30 minutes and an hour, depending on the boiler type and how easily it is accessed. It is a good idea to book your service at roughly the same time each year, often in late summer or early autumn before the heating season starts in earnest, so any issues can be resolved before the cold weather arrives.

Even if your boiler seems to be running perfectly well, an annual service should not be skipped. Many faults develop gradually and are not obvious to the homeowner until the boiler fails completely, at which point the repair is often more expensive and disruptive than the service would have been.

What to expect from your engineer

A good engineer will talk you through what they have checked, flag anything that needs attention now versus something to keep an eye on, and leave you with a written record of the service. They should always be able to show you their Gas Safe ID card on request, and you are entitled to ask to see it before any work begins.

At Harpenden Plumbing and Heating, our engineers are Gas Safe registered and happy to talk through any concerns you have about your boiler's performance during the visit, whether that is a slightly odd noise, higher than usual gas bills, or a room that never seems to heat up properly.

Frequently asked questions

How often should a boiler be serviced?

Once a year is the standard recommendation from manufacturers, and it is also a legal requirement for landlords under the Gas Safety (Installation and Use) Regulations 1998.

What happens if I skip a boiler service?

You risk invalidating your manufacturer's warranty, missing early signs of wear that could lead to a bigger breakdown, and, in the case of a gas leak or blocked flue, a genuine safety risk from carbon monoxide.

What is a Landlord Gas Safety Record (CP12)?

It is the certificate issued after the annual gas safety check required by law for rented properties, confirming all gas appliances and flues are safe. Landlords must provide a copy to tenants and keep records for at least two years.

How long does a boiler service take?

Typically between 30 minutes and an hour for a standard domestic boiler, depending on the model and how accessible it is.

Do you carry out landlord gas safety checks in Hertfordshire?

Yes, we carry out annual gas safety checks and boiler servicing for landlords and homeowners across Harpenden, St Albans and the surrounding Hertfordshire area.