Oil burners and boilers should get a cleaning on an annual basis. Someone should always be present with the service technician while in your home. When paying for a boiler / burner cleaning, make sure that the following is done:
The oil filter is replaced
The burner nozzle is replaced. You may also want to ask the technician to show you the gallons per hour, the type of nozzle and make sure that it is the similar to the one removed
The oil pump strainer is replaced
The chimney and flues are opened and vacuumed clean
The boiler is opened up and brushed / vacuumed
The oil line is purged of air after the parts above are replaced
The chimney cleanout port is closed after cleaning and the flue parts are screwed back together
A combustion efficiency test is performed
Before the technician leaves, you should run the thermostat up and make sure you get heat. This will ensure the technician didn’t inadvertently shut off a pump or close a valve
You should also ask for documentation dated and signed by the technician with the results of the combustion efficiency and date performed