Annual Boiler Service
Keep It Safe, Keep It Efficient

What our engineer actually does

A genuine annual service is a strip down and inspection, not a glance and a sticker. If nobody took the casing off and nobody produced a flue gas analyser, you did not have a service.

Before anything is touched. The engineer checks the boiler location, ventilation and clearances, looks at the flue route and where it terminates, and runs the appliance from cold, because a boiler start-up sequence tells an experienced engineer a great deal.

Gas soundness and supply. The gas installation is tested for tightness, and standing and working pressures are measured at the appliance. An undersized or partly obstructed gas supply causes intermittent faults that get wrongly blamed on the boiler.

Casing off. The burner is removed and inspected for damage, distortion and debris. The heat exchanger is inspected and cleaned. Sooting or scaling is recorded, because both are symptoms of something else rather than problems in isolation.

Electrodes and sensors. Ignition and flame sensing electrodes are cleaned or replaced and their gaps checked against the manufacturer figures. Worn electrodes are the most common cause of ignition lockouts on an otherwise healthy boiler.

Condensate trap. The trap is removed, cleaned and refilled. A trap that has silted up or dried out causes lockouts and, on some appliances, can let flue gases escape. The external condensate route is checked, which matters here in winter.

Seals and gaskets. Every seal disturbed during the service is inspected and replaced if it is not perfect. This is the step cheap servicing skips, and it matters more than anything else on the list, because those seals keep combustion products inside the appliance.

Flue gas analysis. Reassembled, the boiler is run at high and low fire and readings taken from the flue with a calibrated electronic analyser. The ratio of carbon dioxide to carbon monoxide shows whether combustion is clean and within the manufacturer tolerance. It is the most important safety test in the whole service and it cannot be faked.

Flue integrity. The flue is inspected along its accessible length, at the joints and at the terminal, for damage, correct fall, support and clearance from windows, doors and boundaries.

System side. Pressure, expansion vessel charge, pressure relief valve, pump and the condition of the system water. Any magnetic filter is emptied and cleaned. If the water is black or the filter comes out heavily loaded, we will tell you, because that is the start of a much more expensive problem.

Paperwork. A written record of what was checked, what was found, the readings taken, and anything needing attention now or before the next service.

Why annual servicing matters

Safety. A boiler burns gas inside your home. When combustion goes wrong, or a seal or flue fails, the product is carbon monoxide, which has no smell, colour or taste. Flue gas analysis is the test that catches combustion drifting out of specification before it becomes dangerous. Fit an audible carbon monoxide alarm to the current British Standard as well, and test it monthly. An alarm and a service do different jobs, and you want both.

Efficiency. A boiler with a fouled heat exchanger, a partly blocked burner or an incorrect gas rate burns more gas for the same heat. Servicing will not make a boiler better than its design, but it stops it quietly becoming worse.

Warranty. Almost every manufacturer warranty requires an annual service by a Gas Safe registered engineer, recorded and dated, to stay valid. Miss a year and a claim on an expensive component may be declined. Keep the paperwork.

Catching small things early. Worn electrodes, a weeping joint, a tired expansion vessel and a silted condensate trap are all cheap to deal with at a service and all capable of causing a midwinter breakdown if left.

A service and a safety check are not the same thing

People use these terms interchangeably and they are genuinely different.

A gas safety check establishes that an appliance is safe: correctly installed, combustion within specification, adequate ventilation, flue doing its job. It does not include cleaning or maintaining the appliance.

A service includes that check, then adds the maintenance the manufacturer specifies: stripping, cleaning, inspecting and replacing what is worn.

So a safety check tells you the boiler is not dangerous today. A service tells you that and makes it more likely to still be running in February. Landlords legally need the check. In practice you want the service.

Landlords and the CP12

If you let property, you are legally required to have an annual gas safety check on every gas appliance and every gas flue in the property, carried out by a Gas Safe registered engineer, and to keep and issue the record. That record is usually called a CP12, or properly a Landlord Gas Safety Record.

Give a copy to existing tenants within 28 days of the check, and to any new tenant at the start of their tenancy. Keep copies for at least two years. The requirement covers appliances you own and are responsible for, including boilers, gas fires, hobs and cookers.

We carry out landlord gas safety checks across our whole service area and can combine the check with a full service in one visit, which is what we would normally suggest, since the engineer already has the casing off. See our service plans.

Current prices for a service and a landlord certificate are on our boiler service and landlord certificate page.

We also service gas appliances in light commercial settings such as shops, offices and small premises. We do not undertake industrial heating work.

When to book

Autumn. Book in September or October and you get an engineer at sensible notice, before the first cold snap creates the annual rush of boilers that failed the moment they were asked to work hard after five idle months. A boiler that sat unused all summer is exactly the one with a seized pump or a stuck diverter valve, and finding that out in October is an appointment, while finding it out in December is an emergency.

If you have missed autumn, book anyway. A service at the wrong time of year is worth far more than no service at all.

Frequently asked questions

How often should a boiler be serviced?

Once a year, and almost all manufacturer warranties require it. Keep the dated records, because you will be asked for them if you ever claim.

How long should a service take?

Long enough to remove the casing, clean and inspect components, reassemble properly and take flue gas readings. If someone was in and out in ten minutes, they did not do the work described on this page.

What is a CP12?

The common name for the Landlord Gas Safety Record, issued after the annual gas safety check that landlords are legally required to have on every gas appliance in a let property. Tenants must be given a copy.

Will servicing fix a boiler that is already broken?

Not necessarily. A service is planned maintenance. If your boiler has an active fault, that is a repair, and we would rather diagnose it properly than service around it. We can often do both in one visit. See boiler repair.

Does a brand new boiler need a service?

Yes, and in the first year particularly, because that is when warranty terms are most likely to require it. A new boiler still needs its combustion checked and its condensate trap and filter maintained.

Call 01462 506374 to book an annual service or a landlord gas safety check.

Where we cover: We carry out annual boiler servicing across Hertfordshire and the surrounding counties, including Stevenage, Hitchin, Letchworth, Welwyn Garden City, Hertford, Ware, St Albans, Harpenden.