How often should a boiler be serviced?

A gas boiler should be serviced once a year by a Gas Safe registered engineer. Most manufacturers recommend it, and most warranties require it. If you’re a landlord, you also have a legal duty to have a gas safety check done every 12 months, which is a separate thing from a service.

I get asked this a lot around Swindon, usually in October when the heating goes back on and the boiler doesn’t. An annual service won’t stop every fault. It does catch the slow ones, like a perished seal or a condensate trap that’s starting to block. Those are cheaper to sort in September than on a cold night in January.

Why does a boiler need servicing every year?

A gas boiler burns fuel thousands of times a year. Over time the burner and heat exchanger collect deposits, seals dry out and parts wear. None of that is obvious from the outside. The boiler can still heat the house while running less efficiently, or while a fault builds up.

The main reason is safety. A boiler that isn’t burning properly can produce carbon monoxide, which you can’t see or smell. A service checks the combustion and the flue so that problem gets caught.

The other reasons are practical. A boiler in good order uses less gas and breaks down less often. And if it does need a repair, the engineer already knows its history.

Does my boiler warranty need an annual service?

Almost certainly. Most boiler manufacturers make their warranty conditional on the boiler being serviced every year by a Gas Safe registered engineer. The service is usually recorded in the Benchmark checklist that came with the boiler, or registered with the manufacturer.

Terms vary, so dig out your warranty paperwork or look it up on the manufacturer’s website. Check how long you have between services and whether the warranty needs registering. If you miss a service, a claim can be turned down even when the fault has nothing to do with it.

If you’re choosing a new boiler, warranty length and conditions are worth comparing. Our guide to Worcester Bosch, Vaillant and Ideal covers what to check before you choose.

What happens during a boiler service?

Every engineer works slightly differently and every boiler is different, but a proper service normally includes:

• A visual check of the boiler, its pipework and the flue, inside and out
• Checking the flue terminal outside is clear and in a safe position
• Removing the casing (an engineer’s job only) to inspect and clean the burner, heat exchanger and other parts where needed
• A flue gas analysis with a calibrated analyser to check the boiler is burning safely
• Checking the gas pressure and gas rate
• Testing the safety devices and controls
• Checking seals, the condensate trap and pipe, the expansion vessel and the system pressure

At the end you should get a record of what was checked and anything that needs attention. If a part is worn, a good engineer will tell you plainly whether it needs doing now or can wait.

Please don’t take the casing off yourself to have a look. Inside a boiler you’ll find gas and live electrics. That’s why the law requires work on gas appliances to be done by someone on the Gas Safe Register.

What does a landlord need to do?

Landlords renting out a property with gas appliances have legal duties under the Gas Safety (Installation and Use) Regulations 1998. The main ones are:

• Have every gas appliance, fitting and flue they provide checked for safety every 12 months by a Gas Safe registered engineer
• Keep the record of each check for at least two years
• Give a copy to existing tenants within 28 days of the check, and to new tenants before they move in
• Keep gas appliances and pipework maintained in a safe condition

The record is called a Gas Safety Record, and a lot of people still call it a CP12 after the old form name. You can have the check done up to two months before the deadline and keep the original renewal date, so there’s no need to leave it to the last week.

A gas safety check isn’t the same as a service. The check confirms the appliances are safe to use. A service keeps the boiler working well. The table below sets out the difference.

Most of our landlord customers in Swindon and out towards Wroughton and Purton book both on the same visit. It saves arranging access twice.

How much does a boiler service cost?

As an illustrative range only, a standard annual service on a domestic gas boiler in the UK often falls somewhere around £70 to £120. It depends on the boiler, where it’s fitted and what the service includes. A landlord gas safety check is priced separately and depends on how many appliances there are. For a firm price, see our boiler servicing page or get a quote.

Do I still need a carbon monoxide alarm?

Yes. A service reduces the risk, but an alarm is what warns you if something goes wrong between visits. Fit an audible carbon monoxide alarm in the room with the boiler, following the maker’s instructions on where to put it, and test it regularly. In England, rented homes must have a CO alarm in any room with a fixed combustion appliance such as a gas boiler (gas cookers are excluded).

The signs of carbon monoxide poisoning can feel like flu: headaches, dizziness, nausea, tiredness and breathlessness. If the alarm goes off or you suspect CO, get into fresh air, turn off the appliance if it’s safe to, and call the National Gas Emergency Service on 0800 111 999. Get medical advice if anyone feels unwell. The same number applies if you smell gas.