Boiler Maintenance?

My current house has an oil fired hot water boiler - and its not a device I'm terribly familiar with taking care of.  I had to repair some cold solder joints on a control board last year but currently everything appears to be in good working order.  The system fires up and maintains temperature within the set window, the circulation pump fires up when backup heat is called for in the base board radiators, and it runs as needed to provide hot water at the sink.  Beyond the fuel filter I replaced last year, I'm not really sure what I need to do to take care of this system.  My use of it has diminished since I added a heat pump HVAC system to the house, whereas previously this was my main source of heat in the home and domestic hot water.  That said I still have it as emergency or backup heat and it is my main hot water source.

The new house has one. All new to me, so I called the furnace company. He changed the fuel filter and swapped needles in the jet, said it should be good for a few seasons.

I still don't know anything about it though, and it only operates the radiators, we have a separate hot water tank. 

In reply to Nitroracer (Forum Supporter) :

A primary concern will be hard water. Boilers are essentially just heat exchangers, with water as the medium. Any scale or deposits in the tubes will result in a decrease of efficiency. The oil these run on is diesel fuel, at least the ones I've dealt with. Soot can become a big problem if it is not burning fuel efficiently. Main concern with the pump will be pump seal failure; the pumps they use are quite robust. You may also see if the company that built it has a manual available. 
 

All that being said,  they're really pretty simple devices, once you are familiar with the way they operate.

From the burner end of things there are a few things to check:

• Fuel filter - replace annually
• CAD Cell - a little light eye that makes sure it lit when commanded.  Clean the soot and contacts off it annually.
• Nozzle - Confirm you have the correct orifice and cone style as specified by the manufacturer (not uncommon for guys off the truck to swap them with what they have on-hand) and replace annually.  They are cheap enough you can keep a spare.  Like under $15.
• Electrodes - inspect annually and clean the contacts.  Points of electrodes should be evenly pointy like a sharpened pencil and adjusted per the manual.  If they are rounded or flat, replace them and regap.  Clean the contacts.
• Draft - make sure you have good furnace draft when its running.  Can be done several ways.  Old timers set by flame color and feel, the correct way is with gauges.  I set mine by feel and it runs well.
• Monitoring - Keep an ear to it to see if something changes.  Oil burners should start immediately when commanded and shut off immediately when turned off.  Delayed start or after-run is a sign that something is amiss with the nozzle or injection.  Strange whumps, whistles, or bangs is a sign that something is definitely wrong and it needs to be addressed ASAP or you risk a big puff of soot in your house and that will ruin your whole weekend.  Not as big of a deal on hot water as it is on forced air but can still be an issue.  
• For service, that beige box with a motor on it is the nuts and bolts of the oil burning components.  If you google the part and model number on it you can find a service manual and go from there.
• The oil burners are super simple units and cheap to run if well maintainted.  My buddy who does HVAC for a living swears by the older ones, since newer ones are built to a significantly worse price point and sacrifice a lot of long term durability for short term efficiency.