How often should a boiler be serviced?

The short answer is once a year. The longer answer depends on who you are: an owner occupier, a landlord, or someone with a boiler still under warranty. In London there is also the hard water to think about.

The yearly rule, and where it comes from

There is no single law that says every boiler in England must be serviced every year. Instead, three things point to the same answer.

Who	What applies	How often
Landlords	Gas Safety (Installation and Use) Regulations 1998: safety check on each gas appliance and flue	Every 12 months
Anyone with a boiler under warranty	The maker’s guarantee terms	Usually every 12 months
Owner occupiers out of warranty	No legal duty, but maker’s instructions and good practice	Once a year advised

Landlords

The law is clearest for landlords. The HSE guidance for landlords says every gas appliance and flue a landlord provides must have a safety check every 12 months by a Gas Safe registered engineer. The record must go to existing tenants within 28 days and to new tenants before they move in. Records must be kept for two years. A safety check is not a full service, but most landlords book both. Our landlord service and CP12 page explains the difference.

Warranties

Boiler makers set their own conditions. Worcester Bosch says yearly servicing is a condition of its guarantee and must be completed each year. Vaillant says the boiler must be serviced annually by a Gas Safe registered engineer following its instructions. Baxi links its 800 range 10 year warranty to an annual service and a maintained magnetic filter. Viessmann says owners must have the product serviced annually to qualify beyond the first year. Always check your own guarantee certificate, because terms depend on the model and when it was fitted.

Owner occupiers out of warranty

If you own your home and the boiler is out of warranty, nobody will fine you for skipping a service. But boiler makers’ instructions still call for yearly servicing, and a service is the only time anyone measures what your boiler is burning and breathing out.

Why once a year makes sense

Carbon monoxide

A gas boiler that is not burning properly can produce carbon monoxide, which you cannot see or smell. At a service, the engineer runs a combustion test with a flue gas analyser. It reads carbon monoxide and carbon dioxide in the flue gases and shows whether the burner is working as the maker intended. Seals around the combustion chamber and the flue are checked too.

Parts that wear

Seals, electrodes, the condensate trap and the expansion vessel all wear or clog over time. A year is about the right interval to catch them before they stop the boiler.

London’s hard water

Thames Water says all the water in its region is hard. Further south, SES Water supplies hard water from chalk wells. In a combi, scale builds up in the plate heat exchanger that heats your tap water. A yearly check on hot water flow and temperature shows whether scale is building. Our post on London hard water and combi boilers explains what happens inside.

Are there boilers that need servicing more often?

Some situations call for more attention than once a year.

• Heavy sludge. If an engineer finds a lot of sludge in the magnetic filter, they may suggest cleaning it again a few months later, especially after a system clean.
• Repeated faults. If the boiler keeps locking out, it needs a repair visit, not just waiting for the next service.
• Commercial or large boilers. These follow their own maintenance schedules.

For a normal home boiler, once a year is the standard.

What about boilers that are rarely used?

A boiler in a flat that is empty for months, or a holiday let, still needs its yearly service. Parts like seals and the condensate trap can dry out or clog when the boiler sits idle. For landlords, the 12 month safety check applies whether the property is occupied or between tenants, if gas appliances are provided.

What happens if you miss a year

For owner occupiers, the main risk is the warranty. If your boiler breaks down and the maker asks for service history, a missing year could affect the claim. Some makers are flexible if the service was only slightly late. Others are not. Book as soon as you notice and keep the record.

For landlords, a missed safety check is a legal breach. HSE prosecutes landlords who fail to have checks done. In October 2026, HSE reported a landlord sentenced for leaving a gas boiler unchecked for eight years.

Flats and converted houses

In converted houses in places like Clapham, each flat usually has its own combi in a kitchen or hall cupboard. Each one needs its own yearly service. If you own several flats in one building, booking them on the same day keeps all the records on one date. Our Clapham area page covers the cupboard and flue issues common there.

Keeping track

Find the date of your last service on the service record, a sticker inside the boiler cover, or the Benchmark checklist at the back of the boiler manual. If you cannot find any of those, see our post on finding your boiler service history. Then book the next annual boiler service about 12 months on.