What Is a Full Boiler Service? Full vs Basic Service Explained

A full boiler service is a service carried out to the manufacturer's instructions for your model: the engineer takes the case off, checks the gas side, measures how the boiler is burning with a flue gas analyser, inspects and cleans the parts that need it, tests the safety devices and writes the results on a service record. Anything less, such as a look at the outside of the boiler and a check that it fires, is a visual check rather than a full service, even if it is sold as a "basic service".

The word "full" has no legal definition, so it is worth knowing what should be in the visit and what the other names on offer usually mean.

What a Full Boiler Service Includes

A full service covers the gas supply, the combustion, the flue, the safety devices and the condition of the boiler inside the case. The manufacturer's instructions set the detail, and the engineer records what was done.

• Gas tightness and gas rate. The installation pipework is tested for leaks, and the gas pressure and rate are checked against the figures for the model.
• Combustion analysis. A flue gas analyser measures what the boiler is producing, and the readings are compared with the manufacturer's limits.
• Inside the case. The burner, heat exchanger, electrodes, seals and fan are inspected, and cleaned or adjusted where the instructions or the readings call for it.
• Condensate trap and pipe. On a condensing boiler the trap is checked and cleaned so it drains and does not lock the boiler out.
• Flue and ventilation. The flue is checked along its visible route for secure joints and a clear terminal, and any ventilation the boiler needs is confirmed.
• Safety devices and operation. Flame supervision, overheat protection and the pressure relief valve are tested, and the heating and hot water are run to check the boiler works as it should.
• Paperwork. The results go on the Benchmark service record in the back of the manual or on a separate service report, with the readings, the date and the engineer's details.

Our guide to what a boiler service should include goes through each of these checks in more depth.

Full Service vs a Basic or Visual Service

The difference is whether the boiler is opened up and measured. A basic or visual service usually stops at the outside: the engineer looks at the boiler, checks the pressure gauge, fires it up and signs it off.

That kind of visit can confirm a boiler is working today. It cannot tell you whether it is burning gas cleanly, whether a seal inside the case has started to fail or whether the condensate trap is half blocked. Those are the things that cause breakdowns in January and, in the worst case, carbon monoxide.

Watch the wording on cheaper offers. "Safety check", "boiler check", "inspection" and "health check" can all mean different things depending on who is selling them. Some are a genuine service under another name; some are a quick look. The only reliable test is to ask what is included and whether a flue gas analyser will be used and the case removed.

A gas safety check is a separate thing again. It is the legal check landlords need each year and covers every gas appliance, but it does not clean or set up the boiler. Our article on whether a boiler service is the same as a gas safety certificate explains where the two overlap.

Does a Full Service Mean the Boiler Is Stripped Down?

Not always. A full service does not have to mean every part is taken out and cleaned each year; on many modern boilers the combustion reading decides how far the engineer goes.

Many manufacturers' instructions work like this: the engineer takes a combustion reading and inspects inside the case. If the reading is within limits and the burner and heat exchanger look clean, they may not need to be removed. If the reading is out, or there are signs of wear or debris, the engineer goes further and cleans or replaces parts until it is right.

So a short visit on a newer boiler in good condition can still be a full service, as long as the case came off, the analyser was used and the readings were recorded. A long visit where the analyser never came out of the bag is not one, however thorough it looked.

Is the Service in a Plan or a Cheap Offer a Full Service?

It can be, but check rather than assume. The name of the product tells you little; the list of what the engineer does tells you everything.

Before you book, whether it is a one-off visit, a service included in a plan or a discounted first visit, ask four questions:

• Will the engineer remove the case and inspect inside?
• Will a flue gas analyser be used, and will the readings be written down?
• Will the visit follow the manufacturer's instructions for my model?
• Will I get a written service record, or the Benchmark page filled in?

If the answer to any of these is vague, you are probably buying something closer to a visual check. That matters most if your boiler is still under warranty, because manufacturers usually ask for proof of an annual service carried out to their instructions by a Gas Safe registered engineer. The warranty terms for your boiler set out exactly what they expect.

When a Full Service Is Not What You Need

A full service is the right answer for a working boiler that is due its annual check. It is the wrong answer in a few common situations.

• Your boiler has broken down. A service is carried out on a working boiler. If it will not fire, is leaking or keeps locking out, you need a repair visit first; the service can follow once it runs.
• You are a landlord who needs a certificate. The law requires an annual gas safety check of each appliance you provide, recorded on a gas safety record. A full service is good practice but does not replace that record, so book both, ideally on the same visit.
• The problem is in the radiators or pipes. Cold spots, sludge and noisy pipework are heating system problems. A boiler service will not fix them, however thorough.
• The boiler is old and has had repeated faults. A service will keep it safe for now, but it will not change the age of the parts. Ask the engineer for an honest view on its condition, and get that opinion before paying for large repairs.

How to Make Sure You Get a Full Service

Book with a Gas Safe registered engineer, ask the questions above when you book and read the record afterwards. Gas work in your home must be done by a Gas Safe registered engineer, and you can check their ID card on arrival.

Have the make, model and last service date ready so the engineer knows what they are working on. Clear the space around the boiler so the case can come off without moving your things. When the visit is over, the record should show combustion readings, what was cleaned or checked and any advice. If it is a single line saying "serviced, all fine", ask for the detail. Our checklist of signs your boiler service was done properly covers what to look for after the engineer has gone.

If you would like the full version as standard, our annual boiler service in London follows the manufacturer's checklist, with the case off, a combustion analysis and a written record at the end.