Your boiler should be serviced once every 12 months, whether it runs on gas, oil or LPG. Boiler manufacturers recommend it, most guarantees require it, and for landlords an annual gas safety check is a legal duty.
For homeowners, servicing is not a legal requirement. It is still the cheapest way to keep a boiler safe, efficient and covered by its guarantee, and to avoid the breakdown that always seems to arrive on the coldest night of the year.
Why once a year?
A year is long enough for wear to show and short enough to catch it before it causes trouble. Over a heating season, seals perish, the burner and heat exchanger collect deposits, condensate traps clog and sensors drift. None of that is dramatic on its own. Left for three or four years, it adds up to poor combustion, higher bills and a lockout.
Safety is the bigger reason. Any boiler that burns fuel can produce carbon monoxide if it is not burning cleanly or the flue is damaged. The Health and Safety Executive says gas appliances should be serviced and maintained by a competent person, and that oil, wood and coal appliances need servicing too.
Servicing and your guarantee
Most manufacturer guarantees ask for an annual service by a registered engineer, recorded in the Benchmark section of the boiler's manual or logged online. Vaillant, for example, notes that annual servicing by a Gas Safe engineer helps keep the guarantee valid after the first year.
Miss a service and a manufacturer can refuse a claim. On a boiler with a long guarantee, that is a costly gamble to save the price of one visit. Check the paperwork that came with your boiler for the exact terms.
Landlords: what the law says
If you let a property with gas appliances, the Gas Safety (Installation and Use) Regulations 1998 require you to have every gas appliance and flue checked every year by a Gas Safe registered engineer. That annual check is what people call a CP12 or landlord gas safety certificate.
The HSE guidance sets out the detail:
- A gas safety check must be done every year on each gas appliance and flue you provide.
- Give existing tenants a copy of the record within 28 days of the check.
- Give new tenants a copy before they move in. For holiday lets and stays under 28 days, display a copy in the property.
- Keep records for at least two years.
- You can have the check done up to two months early and keep the original deadline, so the date does not creep forward each year.
A safety check is not the same as a full service. The check confirms appliances are safe to use. A service goes further, cleaning and adjusting the boiler so it keeps running well. Many landlords book both on the same visit. Our landlord gas safety certificate page explains how we handle it, which suits holiday let owners along the coast who need everything done between bookings.
What a proper boiler service includes
A quick look and a signature is not a service. A proper one usually involves the following, depending on the boiler and the manufacturer's instructions.
| Check | Why it matters |
|---|---|
| Visual inspection of the boiler, flue and pipework | Spots leaks, corrosion and damage, including salt-air corrosion on coastal flues |
| Flue gas analysis with a combustion analyser | Confirms the boiler is burning cleanly and not producing excess carbon monoxide |
| Opening the case, cleaning the burner and heat exchanger where needed | Removes deposits that cut efficiency |
| Checking gas pressure and rate (or oil pressure and nozzle on oil boilers) | Makes sure the boiler gets the right amount of fuel |
| Testing safety devices and controls | Confirms the boiler shuts down safely if something goes wrong |
| Checking and clearing the condensate trap and pipe | A blocked or frozen condensate pipe is a common winter lockout |
| Checking system pressure and expansion vessel | Low pressure and a flat vessel cause many of the faults people call out for |
| Updating the service record | Keeps your guarantee and records in order |
On an oil boiler, the engineer should also replace the nozzle and fuel filter where needed, check the tank and supply line, and look for water in the fuel. Our oil boiler service page covers that in more detail.
Is there ever a case for servicing more often?
For a normal home, no. Once a year is right. There are a few cases where an extra visit makes sense:
- A commercial or very heavily used boiler, such as a guesthouse running hot water all day.
- An oil boiler that has run out of fuel and pulled sludge from the bottom of the tank.
- A boiler showing warning signs between services: yellow flames, soot, a smell of fumes, or frequent lockouts. Do not wait for the annual visit.
What happens if you skip it?
Plenty of boilers run for a while without a service. That is the trap. The problems build quietly, and the first sign is often a breakdown or a part that has failed because something upstream was ignored. It can also void your guarantee.
If your boiler has not been serviced in years, it is worth booking one now. If the engineer finds problems, at least you know where you stand. If it has already stopped working, see our emergency boiler repair page. For a rough idea of what a visit costs, our boiler service cost page explains what affects the price.
Do not forget the carbon monoxide alarm
A service lowers the risk of carbon monoxide, but an alarm is your warning if something goes wrong between visits. Fit one in any room with a fuel-burning appliance and test it monthly.
Frequently asked questions
Is it a legal requirement to service my boiler?
Not for homeowners. For landlords, an annual gas safety check on every gas appliance and flue is a legal requirement under the Gas Safety (Installation and Use) Regulations 1998. Homeowners should still service yearly for safety and to keep the guarantee valid.
How long does a boiler service take?
It varies with the boiler and what the engineer finds. A straightforward gas boiler in good order is a fairly quick visit. Allow longer if parts need cleaning or replacing, and for oil boilers, which have the nozzle, filter and tank to check as well.
Does a new boiler need servicing in its first year?
Yes. The first service is normally due 12 months after installation, and most guarantees depend on it. Put a reminder in your calendar on the day it is fitted.
Is a landlord gas safety check the same as a service?
No, and it is a common mix-up. The safety check confirms appliances and flues are safe to use. A service cleans and adjusts the boiler so it keeps running properly. Most landlords sensibly book both on the same visit.
How often should an oil boiler be serviced?
Once a year, by an OFTEC registered technician. Oil boilers can build up soot and deposits faster than gas, so skipping a year tends to show up quickly in efficiency and reliability.