What does a service involve?
Clean through the burners, replacing nozzles in the case of pressure jet appliances.
Change relevant gaskets, wicks and rope seals.
Ensure the correct operation of any thermostats and safety devices.
Check oil filters, combustion, chimney performance and condition.
Clean baffles and heat exchangers.
Check for general safe operation and set up of the appliance.
Clean and check the operation of any fans.
Cosmetic checks ie. adjusting doors and lids etc..