An oil boiler should generally be serviced once every 12 months.

This annual service is important because it:

• Ensures safe operation and checks for leaks or carbon monoxide risks.

• Keeps the burner and heat exchanger clean for maximum efficiency.

• Reduces fuel consumption and running costs.

• Extends the lifespan of the boiler.

• Meets most manufacturers’ warranty requirements.

If the boiler is used very heavily (e.g., in large homes or commercial properties), or if you notice smoke, unusual smells, or higher fuel use, it’s worth having it checked sooner.

Typical Oil Boiler Efficiency

• Older standard-efficiency oil boilers (non-condensing, often pre-2005) usually run at 60–75% efficiency.

• Modern condensing oil boilers can reach 90–95% efficiency, but only if well maintained.

• If your boiler hasn’t been serviced in years, it’s common for efficiency to drop 5–15% due to soot, incorrect burner setup, or clogged filters.

How Servicing Improves Efficiency

During a service, a technician will:

1. Clean the heat exchanger – even 1–2mm of soot can cut efficiency by up to 10%.

2. Replace oil nozzles & filters – ensures correct fuel spray and flow.

3. Check combustion with a flue gas analyser – fine-tunes the air-to-fuel ratio for maximum burn efficiency.

4. Inspect seals and flues – prevents air leaks that reduce combustion quality.

5. Adjust the burner – a correctly tuned burner can save hundreds of litres of oil a year.

👉 After a full service, you can realistically expect a boiler running at 70% to rise to 80–85%, or a condensing model to climb back up toward the 90%+ range.

You should always have your oil boiler serviced by a qualified, experienced heating engineer who is OFTEC-registered.

Here’s why:

• OFTEC (Oil Firing Technical Association) engineers are trained and certified specifically for oil-fired systems.

• They’ll issue a CD/11 service record after each service – proof the boiler was inspected and maintained correctly.

• Insurance policies and some fuel suppliers may require proof of OFTEC servicing.

• They’ll carry the right test equipment (like a flue gas analyser) to set your burner up efficiently and safely.

👉 In short: always use an OFTEC-registered technician – just like you’d use a Gas Safe engineer for a gas boiler.

Routine servicing includes cleaning the burner, checking the flue, inspecting the oil tank, and replacing filters or nozzles. Between services, you should also keep an eye on your oil level and any leaks or odours.