What Happens at an Oil Boiler Service? A Homeowner's Guide

Cleaning and inspection

OFTEC says appliances should be inspected and cleaned at a service. Cleaning also gives the engineer a chance to look for tell-tale signs that parts may need replacing, and to inspect the condition of the combustion chamber.

One example OFTEC gives: old steel heat exchangers often show rust marks, which can be a warning that the boiler will soon need replacing. Spotting that early means a replacement can be planned, rather than arranged at short notice when the heat exchanger fails.

Parts that wear out

OFTEC says consumable items such as fuel nozzles and flexible fuel lines should be replaced as required. It explains why they matter: nozzles wear over time, affecting combustion and lowering efficiency; flame sensors can glaze over and make the boiler shut down at random; and worn electrodes can stop it lighting at all.

Grant's instructions for its Vortex boilers say the nozzle and braided oil hose should be replaced every year, unless a long-life hose is fitted, in which case the manufacturer's instructions give its service life.

Why deposits matter

As oil burns, deposits build up on the heat exchanger and the baffles inside the boiler, which can lower its efficiency. OFTEC warns that if they are left for several years they harden, and with some heat exchanger designs the baffles then cannot be removed without destroying them, adding a significant cost on top of the service.

The fuel supply and the tank

OFTEC says that during a service:

• The tank, the fuel supply pipework and components such as filters and de-aerators should be visually inspected, and anything found reported to you.
• Fuel filter elements should be replaced.
• The fuel in the tank should be tested for water contamination.
• Fuel supply pipework that is hidden or hard to reach should be pressure tested at least every five years.

Air supply and the flue

OFTEC says combustion and ventilation air openings should be checked to make sure they are the right size and not blocked. Open-flued appliances should have their flues or chimneys swept regularly, as your service engineer advises.

Sealed heating systems

If your boiler is part of a sealed system, Grant's instructions say the air pressure charge in the expansion vessel must be checked every year, and that not doing so invalidates its boiler guarantee.

Your service paperwork

OFTEC says the registered technician will complete a CD/11, a service and commissioning report, for your records. It records the maintenance done, the results of the combustion tests, and any parts replaced.

The manufacturers ask for a record too. Grant says the details should be entered in the Service Log in the user handbook, and that you will be asked for the boiler's service history if you ever need to use the guarantee. Worcester Bosch says the engineer must complete the Service Record after each service, and that the completed checklist will be needed for any warranty work.

How often, and who should do it

Grant says its boilers must be serviced every 12 months from installation to keep the guarantee. Worcester Bosch says its oil boilers should be serviced once a year, unless the installation or the way the boiler is used calls for more frequent services, by a competent, qualified OFTEC registered engineer.

OFTEC says its registered servicing businesses follow procedures designed so that all parts of your heating system are checked and maintained to industry and manufacturers' standards.

Related advice

• Do I Legally Have to Service My Oil Boiler?
• Oil Boiler Warning Signs: What They Mean and What to Do
• How to Cut the Cost of Heating Your Home With Oil