What Does a Boiler Service Include? The Full Checklist From Our Engineers

A proper boiler service is a strip, clean and test — not a quick look and a sticker. A Gas Safe registered engineer takes the casing off, cleans the combustion parts, measures what the boiler is actually burning with a flue gas analyser, checks every safety device and pressure, then records the readings on a certificate you keep.

That is the short answer. Below is the long one: the checklist our engineers work through on services across Deal, Dover, Sandwich, Canterbury and the rest of East Kent, in the order we do it, and what each check is really there to catch.

What a boiler service actually is

There is no single legal definition of “a service”, which is exactly why standards vary so much. What there is is the manufacturer’s servicing instructions for that specific appliance, and the Gas Safe requirement that any work on a gas appliance is carried out by a registered engineer. A real service follows the manufacturer’s schedule for that model. A bad one is fifteen minutes, no tools, and a sticker on the casing.

The difference shows up on the certificate. If your last service record has no combustion readings on it, no gas rate, and no working pressures, the boiler probably was not opened.

What does a boiler service include? The full checklist

1. Checks before a single screw comes out

We start away from the boiler. Where it sits, what ventilation it has, whether the flue route is still compliant, whether anything has been built, boarded or boxed around it since it was fitted. Kitchen refits are the usual culprit — a boiler that was fine in 2015 now has a fitted cupboard against it, or a new extractor pulling on the same room.

Then we run the boiler as we found it and note the fault history stored in its memory. Recorded lockouts are the best free diagnostic there is: a boiler that has quietly logged the same code twenty times over the winter is telling you something long before it stops. If you have seen a code on the display yourself, our boiler fault code library explains what the common ones mean, and the Glow-worm codes in particular come up constantly around here.

2. The gas side

We check the gas supply and the tightness of the installation, then set the boiler to maximum and take a gas rate. That figure tells us whether the appliance is burning the amount of gas it is designed to burn. Under-gassing is common on older installs with long or undersized pipe runs, and it shows up as a boiler that “does not seem as hot as it used to be” long before it shows up as a fault.

3. Combustion analysis

The flue gas analyser is the single most useful thing in the van. It reads the combustion ratio and the carbon monoxide and carbon dioxide levels in the flue, and it is the check that tells us whether the boiler is burning safely — before and after cleaning, so we can prove the clean did something. Those numbers go on your certificate. If they are out of the manufacturer’s band and cannot be brought back in, the boiler does not get signed off, and we will tell you straight away.

4. Strip, clean and inspect the combustion parts

Casing off. Depending on the appliance and its service schedule that means the burner, the heat exchanger, the condensate trap, the injectors and the ignition and flame-sensing electrodes. The heat exchanger gets cleaned of the dust and debris that builds up over a year of running; the condensate trap gets emptied and flushed, because a silted trap is one of the most common causes of a boiler locking out in cold weather.

Seals get inspected while everything is apart. Perished case seals are a safety matter on a room-sealed appliance, not a cosmetic one.

5. Safety devices and controls

Every safety device gets tested rather than assumed: the flame supervision, the overheat thermostat, the pressure relief valve, the fan and air pressure switch. We check the boiler fires, modulates and shuts down as it should, and that the controls and the room thermostat are actually talking to it.

6. The wet side

System pressure, the expansion vessel charge, and the state of the system water. A flat expansion vessel is behind a huge number of the “my boiler keeps losing pressure” calls we get, and it is a five-minute check that is skipped constantly. Black, dirty system water tells us there is corrosion debris circulating, which is what eventually blocks a heat exchanger or a pump.

7. The flue and its terminal

We inspect the flue along its accessible length and check the terminal outside. On seaward-facing properties in Deal, Walmer, Kingsdown and Thanet we look harder here than anywhere else — salt air is unkind to flue terminals, and we replace corroded ones on coastal homes years before an inland boiler of the same age needs it.

8. The paperwork

You get a service record with the readings on it. If you are a landlord and the visit is a combined service and gas safety check, you also get a CP12 — the two are different jobs and we explain the difference on our landlord gas safety certificates page.

What happens during a boiler service, start to finish

Our engineer arrives, protects the floor, and asks how the boiler has been behaving — that thirty-second conversation regularly points straight at the fault. The boiler runs as-found and the readings are taken. Casing off, combustion parts stripped and cleaned, seals and electrodes inspected, condensate trap cleared. Casing back on, re-fire, second set of combustion readings to confirm the clean worked. Then the wet side, the controls, the flue terminal outside, and the certificate.

If we find something failing, you get told what it is, whether it is urgent, and what it will take to put right — before anything else happens.

How long does a boiler service take?

About an hour for a straightforward combi in an accessible spot. Longer if the boiler is in a boxed-in cupboard, if it is a system boiler with a hot water cylinder and controls to check as well, or if it has not been serviced for several years and everything inside is caked. Be wary of anyone in and out in twenty minutes — that is not enough time to strip and clean a boiler, let it cool, and re-test it.

What is not included

A service is an inspection and a clean. It is not a repair, and it is not a power flush. If a part is found to be failing, replacing it is separate work, charged at our hourly rate with the first hour billable — see our breakdown and repair page for how that works. If the system water comes back filthy, cleaning the system properly is a separate job again. And a service does not extend the life of a boiler that is already beyond economic repair; if yours is at that point we would rather say so, and you can get a real figure from our instant quote.

How often, and what it costs

Annually, without exception, and every year for a rented property by law. There is more on the reasoning in our guide to how often you should service your boiler.

Our boiler service is £90 + VAT, and a landlord gas safety check is the same. If you would rather spread the servicing and maintenance across the year, our BOYLA HomeCare plans run from £9 a month and include the annual service, with no call-out fees for members. Plans begin after a £108 inc VAT inspection. Members on a paid plan also get an emergency response within 24 hours, Monday to Friday.

Book a service with a Gas Safe engineer

Anything involving gas must be carried out by a Gas Safe registered engineer — we are registration number 2836, and have been looking after East Kent boilers for over 25 years. You can read exactly what we do on our boiler servicing and maintenance page, or see the full breakdown of what a service costs in our Kent boiler service cost guide.

To book, call 01304 381999 — a real person answers the phone, and we will get you a date that suits. Autumn books up fast, so if your boiler is due, now is the sensible time.