What is included in a boiler service?

A boiler service is a yearly check by a Gas Safe registered engineer that keeps your boiler safe and running efficiently. It usually costs £70 to £150 and should take at least 30 minutes. The difference between a proper service and a quick look is what happens once the engineer opens the boiler, and this guide shows you what that should be.

At a glance

	What to expect
How often	Every 12 months
Who can do it	A Gas Safe registered engineer (OFTEC for oil)
Time on site	At least 30 minutes, often 45 minutes to over an hour
Independent engineer	About £70 to £130
National firm, one-off	About £130 to £200
What you should get	A written report, including combustion readings

What a boiler service includes

Gas Safe Register describes a service as work to keep an appliance safe and efficient, carried out to the manufacturer’s instructions, and it includes cleaning. Which? and Selectra list the checks a good gas boiler service should cover:

A visual check of the boiler, its pipework and the flame.
The flue, inside and out. The engineer checks it is intact, sealed, properly supported and not blocked, and that the terminal outside is clear.
Combustion analysis. An electronic flue gas analyser goes into the test point on the flue to measure carbon monoxide and how cleanly the gas is burning.
Gas pressure. The engineer measures operating pressure, standing pressure or heat input against the manufacturer’s figures.
Inside the case. With the cover off, they check the burner, heat exchanger, main injector and the spark and flame sensor probes, and clean them if needed.
Seals and gaskets on the case, which stop fumes escaping into the room.
Safety devices and controls. The boiler should shut down safely when it should, and your thermostat and timer should work.
System pressure, leaks and corrosion on the boiler and around it.
A test fire to check it runs properly once everything is back together.
A service report listing what was checked, what was found and the readings taken.

Older boilers can need more dismantling than modern ones, Which? notes.

How to spot a rushed visit

Which? says a good boiler service should last at least 30 minutes. Selectra puts a healthy modern combi at 30 to 45 minutes, and longer if the boiler is over ten years old or a fault turns up. A 20-minute visit is not proof of a bad job, but it should prompt a few questions.

Signs the engineer hasn’t done a full service:

The front cover never came off.
No flue gas analyser was used. It is a handheld box with a probe that goes into the flue.
Nobody went outside to look at the flue terminal.
You got a tick-box sheet with no readings on it, or no paperwork at all.
The engineer couldn’t tell you the combustion results or the gas pressure when you asked.
The visit turned into a sales pitch for a new boiler or a power flush, with no evidence of a fault.

Which? suggests asking what the service includes before the engineer starts, watching the work, and checking the written report is accurate before they leave. If a reading is outside the manufacturer’s limits, the report should say what was done about it.

How often to service a boiler

Once every 12 months. Which? calls an annual service essential for keeping a boiler running safely, and Selectra and Heatable both recommend yearly. Booking in spring or summer is usually easier and cheaper, as Selectra notes prices rise from October to February.

Your warranty. Most boiler manufacturers make an annual service a condition of their warranty. Which? warns that skipping one could invalidate it, so keep every report.

If you rent your home out. In England, landlords must have every gas appliance safety checked every 12 months by a Gas Safe registered engineer, keep the record for two years and give tenants a copy within 28 days, according to the Health and Safety Executive. A gas safety check is not the same as a service: Gas Safe explains that a safety check does not include cleaning the appliance. Many landlords book both on the same visit.

How much does a boiler service cost?

Sources give slightly different ranges, so here they are side by side:

Which? puts a one-off gas boiler service at £70 to £110, averaging about £79.
Selectra gives £70 to £95 from an independent engineer outside winter, £90 to £130 in peak season, and £130 to £200 for a one-off service from a national brand.
Heatable gives £90 to £150 for a standard gas combi, and £110 to £150 in labour for an oil boiler.

Costs run higher in London and the South East. Any repair is extra: Which?’s survey found the average repair after a service cost £156.

Is boiler cover cheaper?

Cover plans usually include the annual service plus repairs. Which? found people paid an average of £183 a year, with some paying up to £300, and prices can rise after the first year. Its research suggests that paying for a yearly service and repairs as needed usually works out cheaper. Cover can still suit you if a surprise bill would be hard to manage.

Before and after the visit

Check the engineer. Every Gas Safe engineer carries an ID card with a licence number. Check the back to confirm they are qualified for gas boilers, or look them up on the Gas Safe Register website.
Clear access to the boiler and to the flue outside.
Mention any faults, like pressure dropping, noises or radiators that stay cold at the top. Our central heating hub covers common problems.
Ask about settings. Which? suggests asking whether lowering the boiler’s flow temperature would save you money. Our heating controls page explains how.
Keep the report with your boiler paperwork for the warranty and for when you sell.

If the engineer says the boiler is near the end of its life, ask for the reason in writing and get a second opinion. Our boilers hub explains what replacement involves.

Questions people ask

Is a boiler service a legal requirement?

Not for homeowners. Landlords must have a yearly gas safety check. For everyone else, an annual service is strongly advised for safety and is usually needed to keep the manufacturer’s warranty valid.

How long does a gas boiler service take?

At least 30 minutes, according to Which?. A modern combi in good condition often takes 30 to 45 minutes. Older boilers and ones with faults take longer.

Is a boiler service the same as a gas safety certificate?

No. A gas safety check, sometimes called a CP12 or landlord certificate, is a set of safety tests on every gas appliance in the home, without the cleaning a service includes. Heatable puts a landlord gas safety certificate at about £100 to £150 in labour. If you rent out a home, ask the engineer to do both on one visit and to give you separate paperwork for each.

Can I service my own boiler?

No. Any work on a gas boiler must be done by a Gas Safe registered engineer. You can bleed radiators and top up system pressure yourself, but leave the boiler casing closed.

Do oil boilers need servicing too?

Yes, every year, by an OFTEC registered technician. Oil boiler services usually cost a little more than gas because they take longer.