Gas boiler servicing

What a service is actually for

There are two reasons to service a gas boiler and they are not equally important. The second is efficiency and reliability – a clean, correctly adjusted appliance uses less gas and breaks down less. The first is that a gas appliance burning incorrectly produces carbon monoxide, and carbon monoxide has no smell, no colour and no taste.

That is why the sequence of a proper service is inspection first, maintenance second. The engineer should be establishing whether the appliance is safe before deciding what to clean, because what the initial checks reveal determines what the rest of the visit involves.

What should happen on the day

1. Check the appliance and its surroundings before touching itFlue route and terminal position, ventilation provision, clearances, the condition of the compartment if it is in one, and whether anything has changed since the last visit – a new extractor fan or a boxed-in flue can both create a problem where there was none.
2. Operational and visual inspectionAppliance run, controls checked, and a visual inspection of the combustion chamber, burner, heat exchanger and any seals.
3. Combustion analysisAn electronic flue gas analyser measures the ratio of carbon monoxide to carbon dioxide in the flue gases. This single reading is the most important output of the whole visit – it tells you objectively whether the appliance is burning correctly.
4. Flue integrityChecked along its accessible length, including any concealed sections where inspection hatches exist. A flue that has separated in a void discharges combustion products into the building.
5. Gas tightness and operating pressureWorking gas pressure and gas rate checked against the appliance data plate, and a tightness test on the installation where appropriate.
6. Safety devicesEvery safety control checked for correct operation – flame supervision, overheat protection, and any other device the appliance relies on.
7. Clean and adjustCondensate trap cleaned, heat exchanger and burner cleaned as the manufacturer specifies, seals checked and replaced where needed.
8. Record and explainWritten record of the readings and the findings, and an explanation of anything that needs attention.

If your service takes ten minutes and produces no readings, it was not one of these.

The combustion reading, and what it means

A flue gas analyser gives a ratio of carbon monoxide to carbon dioxide in the flue gases. It is a direct measure of combustion quality. A correctly burning appliance produces very little CO relative to CO2; an appliance burning badly produces progressively more.

Manufacturers specify acceptable ranges for their appliances, and the industry works to defined thresholds above which an appliance is classified as unsafe. The value of the reading is not just the pass or fail – it is the trend. An appliance whose ratio has crept up over three services is telling you something is degrading, well before it becomes a problem.

Ask for the figures and keep them. It is the same argument as for oil – see what actually happens during an oil boiler service.

What happens if something is unsafe

Where an appliance or installation is found to be unsafe, there is a defined process. The engineer classifies the defect according to industry procedure, explains it, and – with your permission – disconnects or turns off the appliance and attaches a warning label. Where the situation is immediately dangerous, the relevant emergency service provider is notified.

Two things worth knowing. First, an engineer cannot make an appliance safe by ignoring it – the procedure exists precisely because people are tempted to. Second, you are always asked for permission to disconnect; if you refuse, that is recorded and the situation is reported, because at that point it stops being just your decision.

• Immediately Dangerous – a risk of injury or death right now. The appliance is turned off and labelled.
• At Risk – one or more defects that could become dangerous. Turned off with your permission until rectified.
• Not to Current Standards – does not meet today’s requirements but is not dangerous. Recorded and explained, and you decide.

We will always explain which of those applies, in plain language, and what putting it right involves.

Servicing and your warranty

Every manufacturer makes their warranty conditional on an annual service by a competent person, recorded in the benchmark book or equivalent. Skip a year and a seven-year warranty can quietly become nothing at the moment you need it most.

Manufacturers also increasingly require the system to have been cleaned and protected to BS 7593, with inhibitor and often a magnetic filter. A heat exchanger fouled by system debris is the most commonly declined warranty claim there is – see magnetic system filters.

Keep the paperwork with the appliance, not in an email you will not find. A future buyer’s solicitor will ask, and so will the manufacturer.