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This article explains the causes and cures for heating system problems due to sludge in home heating oil tanks, including problems of clogged oil piping, clogged oil filters, oil burner malfunctions, and loss of heat due to sludge in the oil tank. We explain why sludge is a problem in home heating oil & why it leads to loss of heat.
We give first aid advice for what to do if you ran out of heating oil and want to avoid stirring up sludge when oil is delivered. We continue with all of the methods used to avoid sludge problems in heating oil storage tanks: blowing out a clogged oil line, using additives to break up oil tank sludge, installing a Scully Snorkel® to avoid picking up oil tank sludge & water, improvements in oil line filter capacity, steam cleaning oil tanks & lines, & oil tank replacement options.
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Heat System Failure (heat loss) due to Sludge Clogging of Heating Oil Lines, Filters, Nozzles, or Dirty / Debris-Loaded Heating Oil Storage Tanks
Why is Modern Heating Oil Showing a Sludge Problem?
When we serviced heating equipment in the early 1970's, we often found oil fired heating boilers or furnaces that had worked ok for years without any oil filter installed whatsoever!. We were amazed until we learned the history of heating oil cleanliness. We're not talking about the number of BTU's per gallon of heating oil, just how clean or dirty it is.
Before the 1970's oil crisis when much of the heating oil sold in the U.S. was from the middle east, if you put some heating oil in a bottle and examined it, it was a lovely clear yellow color, much like cooking oil. Currently (2008) heating oil in most of the U.S. is black goopy stuff with lots of large molecules that tend to settle out as black sludge in an oil tank, heating oil line, or oil filter.
Heating oil companies are not to blame for this messy stuff. Heating oil is being produced by "cold cracking" - it is chilled and centrifuged rather than distilled into clear oil as in the "old days".
A result of this change in heating oil manufacture is that even overnight in a heating oil delivery truck, a driver may see evidence that some components of heating oil in the tank are settling out as sludge material. The same thing happens in a home heating oil tank. What problems does sludge in an oil tank cause?
Other Caused of Dirty Home Heating Oil - deliberate mix of waste or recycled oil with heating oil
In some locations it may be possible to have received a delivery of contaminated home heating oil. For example, in 2013 the New York Times reported on an investigation of New York heating oil businesses who had "... cheated tens of thousands of customers for years, selling fuel diluted with recycled or waste oil ..." The report described raids on at least five heating oil companies located in and around New York City. Named in the article were Statewide and County Oil and several related or subordinate companies. 
Separately (not part of the raids, commercial and residential building owners filed class-action lawsuits against Castle Oil Corporation and Hess Corporation, making a similar claim - that waste oil had been mixed in with home heating fuel. The mixed, contaminated oil may have been delivered by independent trucking companies hired to deliver oil according to the article, and the report made clear that neither Castle nor Hess had come under scrutiny in the criminal inquiry. 
Watch out: on a much smaller scale, we also have occasionally encountered home or business owners who thought that it was a great idea to dispose of waste motor oil by dumping it into their heating oil tank. Such mixing is not only illegal and stupid, risking loss of heat and related buidling damage, it also contaminates the environment by releasing toxic pollutants such as benzene, toluene, and xylene along with heavy metals such as mercury, lead, arsenic, cadmium, antimony lead, and zinc (all known carcinogens) in flue gases emitted by the heating appliances burning such an oil mix. Don't do this.
Financial Aid for Converting from No. 4 or No. 6 Heating Oil to Cleaner Fuels
The Times article also noted that beginning in 2011 New York instituted the "NYC Clean Heat" program by adopting new regulations to phase out the use of No. 4 and No. 6 heating oils that emit soot and reduce air quality. The NYC Clean Heat program coordinates oil companies, banks, environmental groups and property owners to provide financing intended to help property owners switch to use of cleaner heating fuels like natural gas or low sulfur No. 2 heating oil or biodiesel. 
In addressing heating oil waxing and oil line clogging in cold weather, we discussed use of oil tank additives to reduce the temperature at which this problem occurs. That article is at HEATING OIL CLOUD WAX GEL POINT. But taking our own advice taught a new lesson in oil tank sludge problems.
Sludge causes rapid oil filter clogging: We have seen problems with rapid clogging of heating oil filters and thus loss of heat from sludge that was brought out of an old oil tank and into the filter.
Emergency Measures: what to do if you run have run out of oil and had sludge in your oil tank?
Emergency Procedures to Deal with Oil Tank Sludge & Loss of Heat
Oil companies may recommend that if you have to fill an old maybe sludgy oil tank that was nearly empty, turn off the boiler or furnace for a few hours to let the sludge return to the bottom of the tank (and be sure your heating equipment is fed fuel from the tank top tappings not from the tank bottom tapping.
We are not sure how much trouble someone wants to go through in dealing with oil tank sludge, but because tank replacement is so costly I would take several steps to try to work out the sludge problem without replacing an old sludgy but otherwise good-condition oil tank.
Emergency Oil Tank Sludge Measure - Turn off The Heat: If you know that the oil tank has a sludge problem, if you can't do anything else, at least try turning off the heat for a time during and after the oil delivery. (Don't let the building get so cold that pipes freeze or other damage occurs.) We MIGHT have avoided our oil filter sludge-clog problem discussed above if we'd been able to keep the heat OFF for 3 to 6 hours from the time of the delivery. The idea is to let the worst of the sludge stirred by the delivery settle out to the tank bottom.
Emergency Oil Tank Sludge Has Clogged Oil Lines - Line Blowout: If the oil line(s) from tank to burner become
badly clogged with oil tank sludge, you need help from a heating oil service technician. Sludge often clogs heating oil lines, especially if the oil lines leave the bottom of the oil tank en route to the burner. A service tech finding a clogged oil line (diagnosed by opening the oil line at the burner or by measuring the line vacuum when the burner fuel unit is running) can temporarily "blow out" sludge in the line using a CO2 cartridge and special fittings.
How to Gradually Remove Oil Tank Sludge Without System Clogging
An example of a heating oil additive used by some oil companies to both prevent sludge build-up in modern heating oil tanks and also to (over time) remove sludge in an existing older heating oil tank is "Ultra Guard" a product from Beckett Additives. http://www.beckettadditives.com/
One of our local heating oil delivery companies (Nash Oil, Dutchess County NY) informs us that they are the only local heating oil delivery company who uses this additive in their heating oil. The oil tank delivery truck drivers base their opinion on what they see. We're told that the interior of the Nash Heating Oil Truck Tanks is visibly clean as a result of using heating oil with a "maintenance dose" of Ultra Guard(TM).
Some heating oil technicians may recommend that a "treatment dose" of this additive be tried in an older oil tank which has been suffering from a sludge problem in the tank or oil lines. If this product works as claimed (there is evidence for it) you may be able to avoid an expensive oil tank replacement for an older oil tank which is sludge-contaminated but not leaking. Ask your heating oil company about this or similar products.
Note that this product is not a pour point depressant to avoid waxing or gelling, but sludge, too, can lead to a loss of heat which may be exacerbated in cold weather. (More frequent deliveries, running the oil tank too low on oil, stirring up sludge during oil delivery, clogging the oil burner filter or nozzle as sludge passes through the system all can lead to loss of heat in a building.
What Happens when we use an oil tank additive to break up sludge?
When we added a pour point depressant to our heating oil we hoped it would also break up the sludge - after all, the product also claimed to break up sludge - which sounds good if the oil lines are old and perhaps partly blocked with sludge.
Problems With Heating System Reliability When Heating Oil Additives are Used or Low-Level Oil Tanks are Filled
Watch out: anything that significantly disturbs accumulated sludge in a heating oil storage tank risks sending that sludge-crud through the oil piping to the oil filter and oil burner assembly where clogging can lead to loss of heat and even recurrent loss of heat difficulties. One way that oil tank sludge gets disturbed is when an "empty" or nearly-empty oil storage tank receives an oil delivery. The pouring of heating oil against the oil tank bottom disturbs accumulated sludge there.
When we serviced and installed heating equipment we often recommended use of heating oil additives to remove small amounts of water or sludge in oil storage tanks, or to act as a pour point depressant for outdoor aboveground oil storage tanks. But while these are good products, things didn't always go well. If additives to a heating oil storage tank send increased levels of broken-up sludge through the oil piping too rapidly the risk is that we are sending that crud right into the oil piping, valves, filter, screen, fuel unit and oil burner nozzle: asking for clogs at any point along the way.
This is an excellent approach can keep the heat working while we're waiting for
our sludge solvents to do their job over a longer time. In a property where we were having sludge clogging problems at the filter but where the oil tank was both in good condition and
also difficult to remove even if we wanted to, we took a much less costly approach by doubling the oil filters.
Change oil tank piping pick-up taken off of the bottom of the oil storage tank to enter the tank from a fitting at the tank top. Close off the piping at the oil tank bottom.
Some techs just close the service valve at the tank bottom and remove the piping. I'd also install a cap on the valve outlet to assure that the valve can't just feed oil to the building floor.
Heating oil tank repair, cleaning, & lining companies offer heating or fuel oil storage tank cleaning services that can include pumping out the oil tank, squeegee-cleaning of debris from tank interior, steam cleaning the oil storage tank, and steam cleaning the oil piping lines. More often this service is performed on large commercial-sized (thousands of gallons) oil storage tanks, not on residential tanks. The service will typically guarantee the removal of sludge from the oil storage tank and from plugged sections of heating oil return lines.
Replacing a sludged heating oil tank is a last resort: even though your oil company will take the safe route and recommend this much more costly solution, you may not need to replace your sludge-contaminated heating oil tank UNLESS the heating oil tank is itself one that should be replaced for other reasons anyway, such as:
What the Oil Company Recommends for Sludgy Old Oil Tanks
The oil company will advise you to replace the tank - that's the safest advice for them to give, doesn't cost them a dime, and is most profitable too. The concern faced by the oil company is whether or not the sludgy tank will
The oil company is concerned that these problems are most likely to occur when an oil tank is being stressed by the increase in pressure that occurs in the tank during fill-up. That pressure increase risk is still greater if the tank is not properly vented or if the tank vent is clogged.
Possible Alternatives to Replacing a Sludged Oil Tank
A possible alternative to simply replacing an old oil storage is to have the tank steel thickness measured - if the tank is not corroded and thus not at unusual risk of failure, it makes sense to try to clean out the sludge - a service some oil companies can provide.
If your oil company provides a tank cleaning service we recommend that step. The sludge, debris, and water in the tank are removed by a vacuuming procedure. Because these contaminants are normally sitting on the bottom of the oil tank, this procedure can be used even when the tank is full of heating oil.
You can add an oil tank additive like 4-in-one hot that also breaks up sludge, but if there is a lot of it in the tank it could take a very long time to pass the suspended sludge out and risks clogging the oil filters (and loss of heat) to boot.
When adding an oil tank pour point depressant that also is intended to remove water and also to break up sludge in the oil tank, the risk is that the additional suspended sludge caused by the additive, especially right after filling a low-nearly-empty oil tank will clog the oil filters. See A Guide to No. 2 Heating Oil Waxing, Gelling, or Clouding - for a discussion of additives.
What we recommend if you are unable to find a local company who can remove the oil tank sludge:
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Frequently Asked Questions (FAQs)
Question: would a blocked oil line or sludge problem cause oil smells in my house?
Is this why i smell a oil smell when coming into the house. ? how do i know what caused this? - Anon 5/10/11
Sludge in the oil tank would not itself be the first cause of an oil smell in the home. More likely that odor would be from an oil leak in the piping system or an oil spill during fill-up. ALSO see ODORS FROM HEATING SYSTEMS the article link is found at page top or left
Question: should we switch from oil to natural gas?
A more reliable and much less costly solution is to switch to natural gas. Imagine how much time and effort, not to mention anxiety late at night on cold nights when the heat stops, would be saved by eliminating the messy, apparently insoluble problem in the first place. - John Coburn 5/16/11
Reply: one size does not fit all
Both oil and natural gas as heating fuels have their own individual advantages and disadvantages. But the switch to natural gas is simply not an option in areas where no natural gas service is available. In those locations the switch would have to be from oil to LP gas, requiring the installation of a sufficiently large LP gas tank and appropriate piping, as well as of course complete replacement of the heating equipment.
Question: how do I extend the fuel line up from the bottom of the oil tank to get above the sludge? How can I install an extension without creating an oil spill in the process?
Are there any standard extensions available to extend the furnace fuel line up into the oil tank? For a DIY, a 1/2" copper pipe fits snugly inside a 1/2" iron pipe nipple and the assembly screwed into the tank outlet. Is a 2" extension about right. Unless the tank is empty or nearly so this can be a little messy. - Gil 8/20/11
Of course if you are using a one-line oil system and relying on gravity, depending on where tank and oil burner are located, going to a two-pipe system could require more changes at the fuel unit, and more cost; It is probably possible to pump out the oil tank or use up most of its oil, try blocking the drain at tank bottom from inside temporarily, or just work quickly over a pan large enough to catch the brief oil spill as you remove the old fittings and install the new ones (having them ready and prepped at-hand).
Thanks for your comments. I did ask my oil company if they could pump out the sludge and they said no. I have had this company for a long time and they treat me well so I hesitate to go elsewhere. I used a 3 GPM oil pump to vacuum most of the sludge along the bottom of the tank but did not try to clean very far up the sides. I also pumped out the line to the furnace.
My furnace man did not recommend a line from the top unless we went to a two line system. That got a little pricey for a problem that seemed solvable another way. I did search suppliers of new tanks to see if they offered an extension piece with new installations but did not find any. I'll look further.
At this point there is about 8" of oil in the tank and I can lower a weighted plastic bag over the outlet to help minimize spillage when removing the outlet line. I have a temporary plug ready and then plan to replace the nipple in the outlet plumbing with my made up extension piece. The outlet plumbing includes a shut off valve which also helps minimize spillage. - Gil 8/12/11
Good project Gil. Send us some photos of your procedure and parts solution - it may help other readers. Use the CONTACT link at top, side, or bottom of any page
Mission is accomplished! The extension of the fuel line is in place in the oil tank and all is reassembled. The spillage was minimal, most was caught in a motor oil pan and plenty of newspaper for the splash. I did photograph the extension piece but it is simply a piece of 1/2" copper pipe inside a 1/2" iron pipe nipple. I did secure the copper piece with solder. I can e-mail more details if it would be useful but it may be a week or so. 8/13/2011
Question: two line continuous flow oil piping - do we need an oil filter on the line?
Our oil tank was installed ~ 15 years ago. It has a 2 pipe from the top system to deliver oil to the burner. The Company called it a continuous flow system. Yesterday a new tech came out to service the furnace and said we needed a filter on the line. Is this necessary for a 2 line top system? We lean to the if it isn't broke don't fix it school. - Kathleen 10/25/2012
Kathleen, no modern oil fired heating system should be run without a filter on the supply line ahead of the oil burner itself - doing so is asking for higher service costs and loss of heat as crud in the oil clogs the oil burner.
Question: flame goes out or changes color on my AGA/Kerosene Cooker
THE BLUE FLAME OF MY AGA/KEROSENE COOKER DISAPPEARED AND HEAT WAS REDUCED WHEN I LEFT THE DOOR THAT HOUSES THE BURNER OPEN FLAME RETURNED AND HEAT PLEASE EXPLAIN - Carol 11/20/12
Folks who shout in all caps get tiny font.
I suggest having it examined by an expert. I suggest contacting AGA directly for help and to obtain a technical guide for your heater.
The size of combustion air inlet opening required for your AGA kerosene heater/cooker depends on the model and will be specified in its installation instructions; For example, the similar Rayburn 600K requires 61 cm2 of unobstructed air intake area. The company points out that for this model, an oil fired unit,
You will want to review the installation and operation manual for your AGA heater - easily downloaded from the company's website.
AGA, Station Road, Ketley, Telford, Shropshire, TF1 5AQ, UK, rayburn-web.co.uk
Question: Rayburn Cooker / Heater won't work, is the oil line still clogged?
We're guessing that your Rayburn Heater is a UK device similar to the AGA heater. Rayburn makes cooking appliances, solid fuel, wood, oil, gas and electric heating appliances. Model specifications also vary between in-UK and export equipment.
For example the Rayburn Heatranger includes a cook stove, and it also provides hot water and/or central heating, thermostatically controlled to automatically maintain a constant temperature.
You can contact AGA, Redfyre, or Rayburn directly at AGA, Tel: 08457 626 147, or 08458 152 020, Website: rayburn-web.co.uk. In our references we include more contact information for AGA or Rayburn. 
The company's website provides links to both current and obsolete products' installation manuals and parts lists.
If you have not already done so, I would start by checking or replacing the oil filter that was supplied with your Rayburn heater. Usually the oil filter is located close to the wall where the oil line enters the building, or inside close to the heater itself.
Rayburn also requires a fire-safety heck valve in the oil line; check that your valve is not closed or jammed.
There are other things to check such as for an air leak or failure to purge air from the line after a de-clogging operation; I expect your service tech would also perform a vacuum test on the oil piping system.
Question: how to drain sludge out of an old oil tank
[Photos above & below illustrate this oil tank valve made by Lunkenheimer]
At below left we see the Lunkenheimer oil tank valve in the "closed" position. At below right the reader's photo shows this valve when the valve handle & stem are in the "partly open position" - you can see virtually no change in the actual valve opening.
Watch out: I would not mess with a tank bottom valve at all in this situation; if you start disassembling or unscrewing and your oil tank suddenly spits out its sludge plug, you could have a flood of heating oil on the floor, creating a costly catastrophe.
Reader follow-up: photos of old Lunkenheimer oil tank valve
Before I contacted you I did go to Lunkenheimer's site. Not being a mechanic or engineer I did not see anything there that helped me. Yes, without pictures or a better description it would sound like an air valve and for all I know and what I know about the previous owner of this house it could be. Here are the pictures.
Reply: warnings about messing with the valve at the bottom of an oil tank: oil leak risk
Great photos. Bad news. It looks as if the gate valve is not opening; We could be looking at a backflow preventer mechanism, but I suspect that instead, on this valve the gate stem is broken inside the valve - so it doesn't lift the gate. If the valve seems to turn a bit easily and in particular if in turning the handle the handle stem doesn't move up or down it's probably not moving the actual gate in the valve. On some gate valves the stem will actually turn and even rise up or move down in the valve body, but as the stem end has broken away from the valve gate, the valve never actually opens or closes. This is what I think is happening with your valve.
The oil tank valve photograph below shows this same Lunkenheimer valve in the fully "open" position - actually it's not open.
Advice against trying to replace this bottom-mounted oil tank control valve
Instead of trying to replace this valve, I'd prefer to see the valve opening capped so that it cannot leak at all. Then address the oil tank sludge in the other ways we've discussed.
A plumber, putting down a big pan to catch spilling goop, and who was very nervy and very confident might be willing to try to replace the valve but considering the costs of trying to clean up a big oil spill I figure most will not be willing to touch it. Or an plumber experienced with changing out valves on live water lines might try freezing the short pipe nipple connecting the valve to the tank, then swapping out the valve. But again, it's a risky proposition that, considering how sludge clogs stuff up, probably is not the best approach anyway. I speculate that even if you opened the valve the sludge would clog that opening before accomplishing any useful sludge removal.
BE CAREFUL as I warned before, I'm worried that you'll open the valve and not be able to shut it - flooding the place with oil.
Usually the oil co will pump out as much sludge and water as they can - from a fitting at the tank TOP, then use the additives I cited - like 4 in 1 HOT pour point depressant that also includes a sludge dissolver.
I speculate that the sludge is so goopy that it's not going to flow out of the valve even if you could open it (water would).
If we're working on this because your tank is picking up sludge through the tank top fitted oil line(s) the fix is more often to raise up the lowest end of the tank oil pickup line that inserts into the tank from the top - get it above the sludge level. That may mean you will draw a bit less oil out of the tank before needing a new delivery, but usually that will get you by until you're ready to replace the tank (or if it's tested and found sound you could have the tank professionally cleaned - but we don't ususally find that cost justified for residential oil tanks);
In addition to drawing up the lower end of the oil pickup line from the tank top, on a similar problem system we installed double oil filters, side by side, in parallel, so that we could filter out the stirred-up sludge (from oil deliveries) without having the oil filters clog early. (Oil filters get replaced at annual service). I speculate that valve stopped working a long time ago, after having served for years as a connector to a bottom-connected oil line. The then owners or their service tech realized the danger of trying to change it and instead left it in place, closed, opting to change over to taking oil from the top of the oil tank.
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