An oil fired pressure washer produces hot water by burning oil in a burner to heat the water as it passes through a coil. Where a cold washer cleans with pressure alone, an oil-fired machine adds heat, which dissolves grease, oil, and grime that cold water only pushes around. For heavy, greasy cleaning, that extra heat makes a real difference.
This guide explains how an oil fired pressure washer works, what it burns, and how to get the best and longest service from one.
How Oil Firing Works
In an oil-fired pressure washer, water from the pump passes through a heating coil, a spiral of pipe inside a combustion chamber. A burner fires oil into that chamber, and the flame heats the coil and the water inside it. Because the water and the flame never touch, the water is heated without contamination; it simply flows through the hot coil and exits as hot water at the gun.
The burner is the heart of the heating system. It atomises the oil, mixes it with air, and ignites it, usually with a spark from electrodes. Good atomisation and the right air mix give a clean, hot flame; poor settings produce smoke, soot, or weak heat. Burner setup is what separates a well-tuned oil-fired washer from a smoky, inefficient one.
The result is hot water at a temperature far beyond a cold washer, typically around 200 degrees Fahrenheit or more at the nozzle. That heat is why oil-fired machines are used for degreasing engines, machinery, commercial kitchens, and heavy industrial cleaning, where cold water struggles.
What an Oil Fired Washer Burns
Oil-fired washers run their burner on a fuel oil, most commonly diesel, kerosene, or heating oil. Diesel is widely used because it is easy to find and inexpensive, though it can be dirtier-burning, producing more soot if the burner is not set correctly. Kerosene burns cleaner, with less soot and odour, which suits indoor or cleaner-running applications, but it costs more.
Heating oil, similar to diesel, is another common fuel, and some burners accept a range of these oils. The key is to use the fuel the machine is set up for. Fuels differ in viscosity and burn characteristics, and switching without adjusting the burner can affect flame quality and reliability.
Crucially, the burner fuel is separate from any engine fuel. On a gas-engined hot washer, the engine runs on petrol or gas while the burner burns oil, often from a separate tank. Keeping the two fuels distinct, and never putting the wrong one in the wrong tank, avoids a ruined engine or a dead burner.
Advantages of Oil Firing
The main advantage of an oil fired pressure washer is heat. Hot water cleans grease and oil far better than cold, so an oil-fired machine handles the jobs a cold washer cannot, from engine bays to greasy commercial floors, and it does so without the electrical demand of an electric heater. Oil burners deliver a lot of heat energy from a fuel that is easy to store and transport.
Oil firing also suits remote work. Like a gas engine, an oil burner needs no mains power to generate heat, so an oil-fired washer can run where there is no electrical supply, using its own fuel. That makes it a natural fit for mobile and site cleaning, where an electric hot washer would be impractical.
Finally, oil-fired machines are robust and well suited to heavy, continuous work. Their burners and coils are built for demanding use, and the technology is long proven in commercial cleaning. For professional applications, an oil-fired hot water washer is a workhorse that delivers consistent heat job after job.
Maintenance the Burner Needs
An oil-fired washer needs more attention than a cold machine, because the burner adds parts that wear and foul. The burner nozzle, which atomises the oil, is a wear item and must be replaced periodically, and the electrodes that ignite the flame need checking and correct gap setting. A worn nozzle or misaligned electrode causes poor combustion, smoke, and weak heat.
The fuel system needs care too. Fuel filters and water separators keep dirt and water out of the burner, and a clogged filter or water in the fuel leads to misfires and unreliable starting. Keeping the fuel clean and the filter fresh is one of the most important habits for an oil-fired machine.
The heating coil also needs attention over time. Over many hours it can collect soot on the outside, insulating it and reducing heat transfer, and scale inside from hard water reduces efficiency further, so periodic cleaning or descaling keeps the machine running hot and efficient.
Engine, Pump, and Coil
Around the burner, an oil-fired washer has the same core as any pressure washer: an engine or motor driving a pump, and a coil that heats the water. On gas-engined machines, a petrol engine drives a pump that is usually a triplex pump, chosen for durability under continuous hot-water use. The engine and the burner are separate systems that share the machine but use different fuels.
The coil is central to an oil-fired machine’s performance. It must withstand the heat of the flame and the pressure of the water, so it is made from heavy-duty pipe, often schedule 80 steel, formed into a coil. A well-made coil transfers heat efficiently and lasts for years; a poor one soots up, corrodes, or fails, robbing the machine of heat and reliability.
Together, engine, pump, and coil define the machine’s capability. The engine or motor drives the flow and pressure, the pump delivers the water, and the coil turns it hot. When any of the three is mismatched or worn, the machine underperforms, so a good oil-fired washer is one where all three are built for the heat and duty involved.
Choosing an Oil Fired Washer
Buying an oil-fired washer starts with your work. Match the pressure and flow to the cleaning, the burner output to the heat you need, and the fuel to what you can supply easily. A machine with the right flow and heat for the job will outperform a bigger, poorly matched one, and it will cost less to run.
Consider the format as well. Portable and skid-mounted machines suit a fixed or vehicle-based setup, while trailer-mounted units travel with the work. For mobile cleaning, a self-contained rig with engine, pump, burner, and fuel tanks is the practical choice, because it carries its own power and heat to the site.
Finally, weigh service and parts. An oil-fired machine needs regular burner and coil attention, so choose a model with accessible parts, a clear manual, and available consumables like nozzles and filters. Good support keeps the machine running hot and reliable, which is what you are paying for in an oil-fired washer.
Uses for an Oil Fired Washer
Oil-fired hot water washers are built for the jobs where heat is decisive. They clean greasy machinery and engines, wash down commercial kitchens and food-processing areas, degrease floors and industrial equipment, and handle heavy soot and oil in workshops and plants. Anywhere grease, oil, or fat is the enemy, hot water from an oil burner cleans faster and more thoroughly than cold.
They are also popular in mobile cleaning, where the combination of an engine-driven pump and an oil burner gives a self-contained hot water machine that works anywhere. Fleet washing, plant and construction cleaning, and on-site industrial work all benefit from the heat and independence of an oil-fired washer.
For domestic users, an oil-fired machine is usually overkill; a hot-water unit or even a good cold washer suffices. It is heavy commercial and industrial cleaning that justifies the cost, complexity, and upkeep of an oil-fired hot water pressure washer. Matching the machine to the work is the first rule of buying one.
Running an Oil Fired Washer Safely
Hot water and an open flame demand care. Never refuel the burner while it is running or hot, keep fuel away from the flame and any ignition source, and refuel only in a safe, ventilated place. Exhaust gases from the burner must vent safely, so run the machine where fumes cannot collect, and never operate it in a closed, unventilated space.
The heated water itself is a hazard. At hot-water temperatures, the jet can scald, so keep it away from people and animals, wear protective gear, and be especially careful around the gun and wand. Hot-rated hoses, guns, seals, and gloves are essential, since cold-rated parts will fail under the heat.
The table below sums up the key points of oil-fired ownership.
| Aspect | Detail |
|---|---|
| How it heats | Oil burner flames a coil; water passes through, never touching the flame |
| Fuels | Diesel, kerosene, or heating oil, per the burner’s setup |
| Key wear parts | Burner nozzle, electrodes, fuel filter, water separator |
| Best for | Heavy, greasy commercial and industrial cleaning |
| Safety | Vent exhaust, refuel cold, keep heat-rated parts, avoid scalds |
Handled with care and maintained properly, an oil-fired washer delivers heat that cold machines cannot match.
Frequently Asked Questions
What is an oil fired pressure washer? A hot water pressure washer that heats water by burning oil in a burner to flame a coil. The water passes through the coil and exits hot, without touching the flame.
What fuel does it use? The burner runs on diesel, kerosene, or heating oil, depending on its setup. On a gas-engined machine, the engine uses a different fuel, kept in a separate tank.
How hot does it get? Typically around 200 degrees Fahrenheit or more at the nozzle. That heat dissolves grease and oil far better than cold water.
Is diesel or kerosene better? Kerosene burns cleaner with less soot and odour; diesel is cheaper and easier to find but can soot more if the burner is off-tune. Use the fuel the machine is set for.
Why is my oil fired washer smoking? Usually poor combustion from a worn nozzle, wrong electrode gap, wrong air setting, or dirty fuel. Service the burner and fuel system to fix it.
What maintenance does it need? Regular burner care (nozzle, electrodes), fuel filter and water separator upkeep, coil cleaning or descaling, and the usual pump and engine maintenance.
Can I use it indoors? Only with proper ventilation. The burner exhaust must vent safely, so never run it in a closed, unventilated space.
Is it worth it for home use? Rarely. It suits heavy commercial and industrial cleaning where heat is decisive. For light home use, a cold or simpler hot washer is enough.
Final Thoughts
An oil fired pressure washer is a hot water machine that uses an oil burner to heat water in a coil, unlocking heat that cold washers cannot provide. That heat is what makes it a serious tool for greasy machinery, commercial kitchens, and industrial cleaning, and its independence from mains power makes it a natural mobile workhorse.
Choose it when your work demands heat and you can justify the fuel, complexity, and upkeep. Keep the burner and fuel system clean, replace the nozzle as needed, and maintain the coil, pump, and engine. Above all, run it safely, venting exhaust and avoiding scalds. Looked after well, an oil fired pressure washer delivers powerful, dependable hot water cleaning. For related reading, see our guides on a diesel power washer and a pressure washer with hot water.