What does a boiler service include? A full checklist

A boiler service is a safety and performance check carried out by a Gas Safe registered engineer. It includes a visual inspection, opening the boiler to check and clean key parts, testing how the boiler burns gas with a flue gas analyser, and checking that every safety device works. You should get a written record at the end.

Most manufacturers ask for one every year to keep the warranty valid, and it is the best way to catch small faults before they become a winter breakdown.

What does a boiler service include?

Every boiler is a little different, and the engineer follows the manufacturer’s instructions for your model. A thorough service will normally cover the following.

Before opening the boiler

1. Ask you about any problems. Noises, pressure drops, fault codes or radiators that never get hot.
2. Check the boiler is properly installed and the location, ventilation and clearances are suitable.
3. Inspect the flue inside and outside for damage, correct joints, support and anything blocking it.
4. Run the boiler and check it lights and runs normally for both heating and hot water.
5. Check the pressure gauge and the system for visible leaks or corrosion.

Inside the boiler

1. Isolate the boiler safely and remove the casing.
2. Inspect the main components, such as the burner, heat exchanger, fan, electrodes and seals, for wear, corrosion or debris.
3. Clean parts where the manufacturer requires it. This often includes the condensate trap, which can block and cause lockouts.
4. Check the seals and gaskets so that fumes cannot escape from the combustion chamber.
5. Refit everything and check that the case is sealed correctly.

Testing

1. Flue gas analysis. A calibrated analyser checks the combustion readings against the manufacturer’s figures. This shows whether the boiler is burning gas safely and efficiently.
2. Gas pressure and gas rate checks to make sure the boiler is getting the right supply.
3. Gas tightness. The engineer checks for leaks on the gas connections they have disturbed.
4. Safety devices. Checking that the flame sensing, pressure relief valve and other protections work as they should.
5. Expansion vessel and system pressure where the boiler and manufacturer call for it.
6. Controls. Checking that the thermostat and programmer call the boiler on and off.

Part of the service	Why it matters
Flue inspection	A damaged flue can leak carbon monoxide
Flue gas analysis	Confirms safe, efficient combustion
Condensate trap clean	Prevents blockages and lockouts
Seal checks	Keeps fumes inside the boiler
Safety device tests	Makes sure the boiler shuts down if something goes wrong

How long does a boiler service take?

A straightforward annual service on a well-maintained boiler commonly takes around an hour, but it varies. Older boilers, boilers that have not been serviced for a while, or ones where the engineer finds a problem can take longer. Allow time for the engineer to run the boiler before and after.

Is a boiler service needed for my warranty?

For most new boilers, yes. Manufacturers generally make an annual service by a Gas Safe registered engineer a condition of the warranty, and they may ask for proof if you make a claim. Check the terms that came with your boiler, because the exact requirements vary.

When we fit a new boiler, you get up to 15 years warranty on boilers, subject to the manufacturer’s terms. Keeping up with annual servicing is what keeps that warranty in place. Our boiler warranty guide explains what to look out for.

What do you get after a boiler service?

• A service record or report listing what was checked, the readings taken and anything that needs attention.
• An update to your boiler’s logbook or service history, where your boiler has one.
• Advice on anything found. For example, a worn part that should be replaced before winter, or a recommendation such as a magnetic filter if there is sludge in the system.
• A clear warning if anything is unsafe. If an engineer finds a dangerous fault, they must tell you and may need to switch the appliance off until it is fixed.

Keep these records somewhere safe. You will need them for warranty claims, and buyers often ask for them when you sell your home.

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

Not quite. A gas safety check is a safety inspection, and for landlords it is a legal requirement every year. A service goes further, with cleaning and maintenance to keep the boiler running well. Many landlords book both at the same visit.

How often should you service a boiler?

Once a year is the usual recommendation, and it is what most manufacturers ask for. Autumn is popular because faults show up when the heating comes on, but any time of year works. Our guide on how often to service your boiler covers this in more detail.

When to call an engineer between services

• The pressure keeps dropping
• The boiler shows fault codes or locks out
• You notice a yellow or orange flame, soot marks or a smell of fumes
• Your carbon monoxide alarm goes off. Leave the property and call the National Gas Emergency Service on 0800 111 999

To book, use our boiler servicing page or call Lee on 020 8050 5913. Our current rates are on the prices page, and we service boilers across South and South West London and north Surrey, including homes in Clapham and Balham.