Multi/Waste Oil Boilers From 27kW to 1,275kW Output

KWOB Multi Waste Oil Boilers,Multi Oil Boiler,waste oil boilerWaste oil boilers deliver an efficient way to recycle waste oils as a free fuel source to generate heat and hot water, which can be used to heat garages, workshops, warehouses, greenhouses to name but a few, within the broad range of applications it can be used for. Our German made waste oil boilers are designed for the unique demands of providing water heating systems run on waste engine oils, hydraulic oil, vegetable oils, bio-diesel and a range of other fuels. Convert all these free or low cost fuels into clean, usable heat and virtually eliminate your fuel costs!

At a time of rising fuel costs, the Kroll universal/waste oil boiler, which can burn nearly all vegetable, animal, conventional and waste oil, will save you money and provides you with flexibility in choosing your preferred fuel source.

The Kroll series of waste oil boilers are designed for perfect compatibility with Kroll waste oil burners, providing a complete and proven solution. These waste oil boilers are made in the EU and exported worldwide. They combine exceptional prices with excellent quality for unbeatable value.

In more recent times we have seen a large increase of people using vegetable oils as a fuel, this is a very green option as its renewable and also is CO2 neutral. Our burner was one of the first, of the very few to gain the DIN standard for use on rapeseed oil, which is used extensively as fuel in countries such as Denmark and Sweden due to the high relative prices of energy within those regions

Did you know that you could significantly reduce or even eliminate your heating costs by utilizing waste oil boilers or heaters for your heating needs?  Waste oil boilers and heaters fuelled with used oils such as used vegetable oils, recycled oil, used motor oils and hydraulic oils –

What can the Kroll Multi / Waste Oil Burner use as a fuel-

  • 35/28 second Heating Oil/Diesel
  • Processed Fuel Oil ( PFO )
  • Rapeseed Oil
  • Linseed Oil
  • Certain Vegetable Oils
  • Used Engine Oil (subject to licensing control)  
  • Hydraulic Oil
  • Bio Diesel   

The Waste Oil Boiler, is a steel pressurised boiler for operation of water temperatures above 50C, and benefits from the following features –

Reversed flame combustion chamber for high efficiency, efficient combustion, low emissions and lower flue gas temperature
Highly resistant to condensate thanks to:
– Furnace misalignment against the outer shell
– Patented fin effect on the welding seams of pipes onto the rear tube plate
• Anti-condensing helicoidal turbolators
• Fully insulated design prevents heat loss, due to the extensive insulation (60 mm) of rock wool surrounding the boiler body and the ceramic fibre insulation on the door
• Adjustable door with double opening (left or right)-with easy access through the front door to all parts of the boiler chamber for quick, easy cleaning and ash removal
• Separate control panel with simple and clear information and controls
• Maximum working pressure: 6 bar; it is possible, under specific request, to provide a Maximum Working Pressure of 7 , 8 , 9 or 10 Bar

Kroll Waste Oil Boiler

** For boilers above 200kW,  please contact us directly

Download Waste Oil Boilers Brochure

Waste Oil Boilers / Multi Oil Boilers – Thing’s you need to know

General Waste Oil Boiler Info –

1. When burning correctly, these units burn as clean as a standard oil boiler, with no plumes of black smoke etc
2. These waste oil boilers are not suitable for installation in a house, as the pre-heating of the oil, can sometimes cause a smell. They should be sited in a separate building, such as a boiler house / garage etc, and the warm water is brought via pipes into the house or premises.
3. These waste oil boilers are not room sealed / balanced flue thus shouldn’t be fitted in within residence, as they require a combustion air source i.e. ventilation

Fuels – Waste Oil or Standard Oil – these Multi Oil Boilers will burn both

1. The burner attached to the waste oil boiler, is in reality a multi oil burner, which means it will burn gas oil (sometimes referred to 35 second oil or as red diesel), kerosene ( 28 second oil), waste engine oil (with some conditions – see point 2 ), transmission oil, vegetable oil, and used vegetable oils ( with some conditions – see point 3 )
2. If you are using waste engine oil, then if you have over 50% synthetic oil, and by this we mean any oil that has the word synthetic in it , to mineral oil , then you need to add 15% gas oil or kerosene to the waste engine oil. This needs to be agitated, so it mixes with the engine oil (normally done, by dropping a compressed air line into tank, for approximately ½ hr after introducing the gas oil into the waste engine oil). This needs to be done on a monthly basis in the heating season, as the diesel will settle to the top of waste oil over this period and needs to be remixed
3. If you are using waste vegetable oil, then the fats have to be removed, via settling out, the oil should also be filtered down to 5 micron – please see separate data sheet on this subject

Maintenance of your waste oil boiler –

1. “You get nothing, for nothing” as the saying goes, and if you are burn waste oil, then they are not made to a definite BS / EN standards, which specifies their filtration level, their calorific value etc. Waste engine oil often has small metal particles suspended in the oil, which should lie as a fine white dust if the boiler is burning correctly. This builds up over a period of time, how quickly this does depends on how “dirty” the oil is (remember it’s your oil, not mine – I can’t tell you ! ) thus we recommend opening up an inspecting the boiler every 300 burning hours ( roughly 6 weeks in the winter ) and cleaning the combustion chamber , and boiler tubes – this should take approximately ½ to ¾ of an hour of your time – if so required- if it isn’t close the boiler back up and check again in another 6 weeks . If you are not prepared to do this, to ensure the correct operation of the boiler, please buy a standard oil or gas boiler of us, and don’t moan to me regarding how much your fuel bills are !!! , you get free heat via your waste oil, it needs you time!!
2. These waste oil / multi oil boilers are an “oil burner “not a miracle worker, and things like brake fluid and clutch fluid, should not be burnt as they cause problems to the burner ( they destroy the rubber seals, that we use in our nozzles, and crystallize up, causing blockages in the nozzles and pipes of the burner – they are fluids not oils !!!!!
3. Also no petrol or paint thinners either!!! We use a pre-heater to heat the oil up to 75 C ish for waste engine oil , or up to 140 C for vegetable oil . This will ignite the fluids and cause a fire!!!

If you are not prepared to do this, to ensure the correct operation of the waste oil boiler, please buy a standard oil or gas boiler from us, and don’t moan to us regarding how much your fuel bills are !!! , you get free heat via your waste oil, it needs your time!!

The basis of this information, is to let you know the pro’s and con’s of burning waste oil, and the fuel bill savings you can achieve, please remember that you could be saving thousands of pounds per year and to let you, the customer, decide if a waste / multi oil boiler is right for you.

Multi Oil – Waste Oil Tank – 100 Litre Storage 

We highly recommend that you use our oil tank with our multi / waste oil burners, which are fitted to our automatic waste oil warm air heaters or our multi / waste oil boiler packages.

The purpose of this tank is twofold –

  1. It can be used as your oil tank for your fuel, negating the need for an external oil tank, depending on the size of your waste oil burner, it may need topping up every couple of days or may be every week dependant on your usage.
  2. You can also use this as in intermediate oil tank , from your external oil tank and there are numerous advantages for this –
  • You have a quantity of oil, which is stored internally within the building, which should mean that the oil is warmer than the oil in the external oil tank. This helps the burner , as the oil does not have to be heated as high
  • The tank has a “floating oil suction line “(see picture), with a filter attached. This takes the cleanest oil as it floats on top of the oil

  • The oil is then pumped , and controlled by the burner , via a filter , ensuring you have the cleanest possible oil to the burner
  • It is a fully automatic operation , the burner controls the pump on demand

Coupling the 100 litre tank to a bulk external oil tank –

This is an easy thing to do –

We supply a kit, that consists of a solenoid valve, and two float switches. These are to be installed to suit site conditions i.e. where ever your incoming pipework dictates

You need to make a tapping / tank connection on one of the walls of the 100-litre oil tank, for the oil supply that will be controlled with a solenoid valve.

You also need to make one tapping below the incoming oil line, which will have the solenoid valve attached to it, this is for the “control float switch “, which opens or closes the solenoid valve – for safety, the oil solenoid valve we supply is a normally closed valve, which means that the control float switch, energises the solenoid valve when more oil is required, and cuts the power to it, when the float switch is satisfied

The second float switch, which we call the “safety or alarm float switch” needs to be positioned at the top of the tank. This float switch can activate an alarm bell (supplied by others) and also be wired to kill the electric supply to the waste oil heater or burner. It is in effect an alarm system to notify you should the solenoid valve ever fail


Waste Oil Boiler , now with the option of a built in compressor up to 116kW, the range extend to 1,110kW ( external air source required after 116kW )

Here at Flexiheat , we are always moving our product development forward , and due to many requests , we now have a waste oil boiler and burner combination , that has a built in compressor , thus eliminating the need for an external air source. This means that burner only produces the air that is required when the burner is in use, this results in large running cost reductions, as you don’t need a compressor running 24 hrs / 7 days a week  to supply the air to the waste / multi oil burner attached to the boiler. This option is available on our waste oil boiler packages with an output of up to 116 kW / 395,792 BTU’s . At present after this kW output then an external air supply is still required . These Flexiheat Multi Oil Boiler Packages are now designated the “FMOB” range , and if the unit has a “C” after the model number , then this means that the burner has a built in compressor.The full range of multi/waste oil boiler goes up to 1,100 kW output , but after 116kW output , you do require a compressed air supply , with a 1.5 Bar pressure and the volume of air require varies with regards to the burner output.

A Brief overview of the most common waste oil boilers are listed below,for above 233kW , please contact us direct

Waste Oil Boiler

Download FMOB Boiler Brochure

If you require any further assistance with our Waste Oil Boilers / Multi Oil Boilers  or any of our products, please click here to contact us via email or call us direct on 01202 822221