After how many oil tank fills do I do a oil boiler clean out / tune up?

In general it's recommended to do maintenance every 1000 gallons or every year. I strongly recommend not attempting to do this yourself unless you want to invest in some expensive tools and training on how to use them. You will need a digital combustion analyzer, oil pump pressure/vacuum testing manifold, smoke pump, digital multimeter, air and water pressure gauges, air compressor, several hand tools and probably some things I forgot to list.

You won't be able to find anyone who will do a PROPER boiler maintenance for $50-$100. You would be better off finding someone like me who charges more than that to use my thousands of dollars worth of tools to ensure the boiler is running safely, reliably and efficiently as possible.

A proper annual service is 2 hours minimum and should be done every year. I like doing them in the spring so the boiler sits clean all summer in what are usually humid basements here in the northeast.

This is true IF you have a soiled heat exchanger. Then you need to have the heat exchanger brushed and vacuum cleaned. When I learned to do oil burner maintenance in the 1970s we were expected to complete 4 residential oil burner maintenances per 8 hour day. That allows for 1/2 hour driving time between visits and 1.5 hours per service. We were taught "Efficiency Service". that means being stocked and prepared each morning. Have a tool box that could hold combustion kit, filters, nozzles and gaskets that every standard oil burner tune up required.

1. Operate the burner for a minute or so to make sure there was nothing wrong before you take anything apart.
2. Take the burner apart and soak all the dirty parts in jiffy juice (nasty cleaner SidHarvey sold).
3. Take the heat exchanger covers off and vent connector apart to vacuum clean the chimney base nad vent connector pipe
4. Brush the heat exchanger and vacuum clean
5. Put the heat exchanger covers and vent connector back in place and cement the vent connector to the chimney base.  Seal all the heat exchanger covers as needed
6. Clean up area around the heater and wash hands of soot
7. Work on oil burner to include
   1. Remove nozzle and clean assembly 
   2. Clean & inspect electrodes
   3. Install new nozzle in clean assembly
   4. Replace cleaned electrodes and adjust to specifications
   5. Brush dirt and lint from burner fan
   6. Replace the cleaned pump screen with a new gasket or install a new pump screen if the old screen was really bad. 
8. Reassemble burner
9. Replace oil filter and prime the oil pump.
10. Test fuel pressure and test safety lockout timing on the primary control
11. Remove the pressure gauge and connect the high pressure line to the nozzle assembly.
12. Fire burner and test combustion with instruments,
    1. Smoke test… adjust burner as needed
    2. Stack temperature test
    3. Draft test. Adjust barometric as needed
    4. CO2 test… adjust burner as needed
    5. Final smoke test to verify clean burning flame
13. Put tools away and clean the heater area 

All this was done with one additional trip to the truck to minimize time on the job since all the necessary tools were brought in on the first trip.  The vacuum cleaner and trash can was brought in on the second trip, along with the nozzle and oil filter if your tool kit didn’t have the proper nozzle and filter already in the toolbox 

There are 2 trips back to the truck to put the vacuum cleaner and trash can away, prepare the invoice receipt for the customer signature and calculate payment if needed.  Last trip included the tool box and anything that you could not take on the first trip plus the customer's signature or payment.  This was a great way to learn to tune up a heater because you had an order to each task and did not waste time with 10 trips to the truck for each different procedure. Most tuneups were finished within 1.5 hours.

Today However I have found that proper adjustment of the burners are leaving the heat exchangers free of soot buildup. This means the the vacuum cleaner stays in the truck and you save up to 45 minutes on the maintenance time. You still need to remove the vent connector and inspect the chimney base, take the heat exchanger covers off and inspect the flue passages, then put that back together and seal up the covers and connector to chimney with cement.

All the burner stuff still gets done but because you did a great job last year, you don't need 2 hours this year. A skilled mechanic can get the job done completely with 45 minutes if the heater was properly serviced the previous year. Maybe every 3 to 5 years the heater will need the complete brush and vacuum treatment but I find that doing it right the first time saves time and $$$ in the long run.

I have found new customers, (that leave the incompetent competition) with poorly maintained equipment. It may take me 2 or more hours to do the proper tune up and cleaning. But each year after that they are a pleasure to maintain.

Half a day or more? There are probably some folks on this forum who could commission a new boiler in that amount of time.

@EdTheHeaterMan said:

 It is amazing how much Oil Heat has changed since those old ACME, QUIET HEAT,  ARCO and PETRO soot making oil burners.

Speaking of cleanliness, it's also amazing how modern instruments have made it easier to adjust oil burner combustion properly. I don't know what they used in the bad old days, but I do know we had a tragedy in our house in the late 1970's or early 1980's when we came back from a family vacation.

My mother walked in the door and noticed everything in the house looked rather dingy. She soon realized the entire inside of the house was covered in a fine layer of soot. We had had a "puffback," which I (and my parents) had never heard of until that day. My mother cried.

Every surface in the entire house had to be washed and/or professionally chemical-cleaned. It took weeks. Eventually everything got cleaned, but it was a nightmare for my mother.

I don't know what caused the soot buildup in the chimney that resulted in the puffback, but I'm guessing our boiler guys just eyeballed the flame and called it good. Also, my parents had never been told that the chimney for an oil burning boiler neededs to be cleaned. So no one ever looked inside the chimney and saw the soot buildup. Thank goodness the days of adjusting combustion by eyeball are gone…I hope.

Oil gets a bad rap for being dirty and soot and some of that was true in the old days. But better some soot than CO poisoning from gas.

I am NOT saying oil can't make CO. Its a fossil fuel so it can. But in almost all cases with oil the soot will be the evidence of poor combustion where with gas you usually get no such indication.

@jesmed1

In the old days it was a Bacharach (or Dwyer) wet kit. They still sell them. It was in the Bacharach kit like a plastic hollow dumbbell with a fluid in it that was replaceable. They made models that measured O2 or CO2. They also made a "monixor" for measuring C0 that used a 1 time glass tube and a smoke gun for measuring smoke.

A sample tube went in the flue pipe and attached to the dumbbell. The hose had a squeeze bulb on it that you would squeeze 18 times to that a flue gas sample and put it in the dumbbell. Then you turned the dumbbell over several times to mix the fluid and flue gas sample

They worked and were reasonably accurate. The problem was it was time consuming. Very difficult to get enough run time (especially during the summer) to be able to test without overheating the house.

You would frequently turn up the high limit to get more run time but then you would be off on limit.

See the attached

If oil is running right you should never have to clean the chimney. Every complains about the pin boiler but then they go out and install them.

I don't see the issue. The Weil McLain Gold has been out since at least the mid 80s and is a proven good boiler.

If it wasn't they wouldn't be still making them.

What cracks me up is when you go into a really old job where they have an old boiler and maybe an old burner or a newer replacement. (9 out of 10 will say "its junk, get rid of it this thing is an antique its old"

If it was junk it wouldn't have lasted so long