How often should you service your boiler
Once a year. Every year. That is the whole answer, and almost every boiler manufacturer in the UK says the same thing in the warranty paperwork.
The longer answer is worth reading, because plenty of people skip the service, save £140, and then pay £2,500 for a new boiler two winters later.
Why annual servicing matters
Your warranty depends on it
Manufacturers give long warranties on new boilers. Vaillant, Worcester Bosch and the rest will happily cover a boiler for seven or ten years. Read the terms and you will find the same condition every time. Annual servicing by a Gas Safe registered engineer, recorded in the benchmark logbook.
Miss one service and the manufacturer can refuse a claim. A failed heat exchanger costs more than a decade of servicing. This is the single most expensive corner anyone cuts in their home.
Safety
A boiler burns gas inside your house. When combustion goes wrong, it produces carbon monoxide, and carbon monoxide kills people who never knew anything was wrong.
An engineer measures combustion with a flue gas analyser, checks the flue is sealed and venting correctly, and confirms the safety cut off devices work. None of that is visible from the outside. A boiler can look perfectly normal and be dangerous.
Running costs
Boilers lose efficiency gradually. Sludge builds in the system, the heat exchanger fouls, the condensate trap partially blocks, gas pressure drifts off spec. Each of those makes the boiler burn more gas to produce the same heat.
A serviced boiler running at its designed efficiency uses noticeably less gas than a neglected one. Over a London winter that difference pays for a good chunk of the service.
Small faults stay small
Engineers spot the corroded fitting, the weeping pump seal, the expansion vessel that has lost its charge. Fixing those in September costs a fraction of what they cost when they fail on Christmas Eve and take the heating with them.
What actually happens during a boiler service
A proper service takes 45 minutes to an hour. If someone is in and out in ten minutes they have looked at the boiler, not serviced it.
Here is the work.
- Visual inspection of the boiler, the flue, the pipework and the surrounding area.
- Removal of the casing so the engineer can see the components.
- Combustion analysis with a calibrated flue gas analyser, comparing readings against the manufacturer specification.
- Checking gas pressure and gas rate.
- Inspecting the heat exchanger for corrosion, scale and blockage.
- Cleaning the condensate trap and checking the condensate pipe runs freely, since a frozen or blocked condensate is the most common winter breakdown.
- Testing safety devices, including the overheat thermostat and the flame supervision device.
- Checking system pressure, the expansion vessel charge and the pressure relief valve.
- Checking seals and cleaning any components that need it.
- Completing the service record in the benchmark logbook and giving you a written report.
If the engineer never takes the casing off, you have not had a service.
What a boiler service costs in London
We charge £140 plus VAT for a domestic boiler service on any major brand.
Landlords who also need a gas safety certificate should book both together for £220 plus VAT. Same engineer, same visit, one appointment to arrange with the tenant. See the full pricing page for everything else.
Our Gas Safe engineers work at £120 per hour plus VAT for domestic work, so if the service uncovers a repair we quote it before doing anything.
Book it in summer
Nobody thinks about the boiler in July, which is exactly why you should.
Engineers are quiet in summer, so you get an appointment within days rather than waiting. If the service finds a problem, you have months to sort it out rather than sitting in a cold house in January. And if your boiler has spent the summer idle, a service before the heating season starts catches the seized pump or the stuck diverter valve before you need them.
Set a recurring reminder for the same month each year. Or let us track it for you. We remind the households and managing agents on our books when a service falls due.
Landlords need two things, not one
A boiler service and a gas safety check are different jobs.
The CP12 gas safety certificate is a legal requirement for rented property. It confirms appliances are safe. It does not clean the boiler and it does not satisfy the manufacturer warranty.
The service maintains the boiler. It is not a legal requirement, but it protects the warranty and reduces the chance of a tenant ringing you at midnight in December.
Do both. Book them together and pay less than you would for two visits. Our gas services page covers the certificate side in detail.
Signs your boiler needs attention before the service is due
Do not wait for the annual visit if you notice any of the following.
- The pressure gauge keeps dropping and you keep topping it up.
- Radiators are cold at the top or take an age to heat up.
- The boiler locks out and shows a fault code.
- Banging, whistling or gurgling from the boiler or the pipes.
- The pilot light or flame burns yellow or orange rather than crisp blue.
- Yellow or brown staining on the boiler casing.
- Hot water runs hot then cold then hot again.
- Any smell of gas at all.
The last two on that list mean stop reading and pick up the phone. If you smell gas, turn the supply off at the meter, open the windows, do not touch any electrical switches and ring the National Gas Emergency Service on 0800 111 999. Then call us.
Everything else on the list is a repair job. Our boiler and heating engineers work on Vaillant, Worcester Bosch, Ariston, Gledhill and the rest, and we carry common parts on the van.
What if your boiler has never been serviced
Plenty of boilers in London have not been touched in five years. They still work. That does not mean they are safe or efficient.
Book a service anyway. The engineer will tell you honestly what condition the boiler is in. Sometimes that means a clean, a new seal and a system that runs better than it has in years. Sometimes it means a boiler that has reached the end of its life and is now costing you money every month it stays in place.
Either way you will know, which beats guessing while the heating limps through another winter.
An older boiler with a poor service history is also a good candidate for a powerflush, because years of sludge in the radiators strangles the system and shortens the life of the new boiler if you do not clear it first.
Frequently asked questions
How long does a boiler service take?
Between 45 minutes and an hour for a standard domestic boiler. Older or more complex systems take longer.
Is an annual boiler service a legal requirement?
Not for homeowners. Landlords must arrange an annual gas safety check by law, and separately, almost every manufacturer warranty requires an annual service.
Will skipping a service void my warranty?
In most cases yes. Check the terms that came with the boiler. Manufacturers ask for proof of annual servicing before they honour a claim, and a missing year is enough for them to refuse.
Does a new boiler need servicing in the first year?
Yes. The warranty clock starts at installation, so the first annual service falls 12 months later. New boilers rarely have anything wrong with them, but the record matters.
Can I service my own boiler?
No. Working on gas appliances without being on the Gas Safe Register is illegal and dangerous. You can help by checking the pressure gauge, bleeding radiators and keeping the condensate pipe clear.
What if the boiler is over 15 years old?
Keep servicing it while it runs well, but start planning. A boiler that old runs at much lower efficiency than a modern condensing model and parts get harder to source. A new boiler installation typically costs between £2,000 and £3,500 including VAT.
