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Posted: 08/11/2018

Oil Aga range cooker “sooting up”? Can we blame the EU for dodgy oil and premature carboning?

Oil Aga range cooker “sooting up”? Can we blame the EU for dodgy oil and premature carboning?

An oil fired Aga is a simple device originally designed many decades ago to provide cooking and heating in the kitchens of rural homes. One problem with oil fired Agas and Rayburns is an occasional increased need to service an appliance due to premature carboning. This has been called the Aga Saga and is often blamed by Aga owners and engineers on fuel and fuel quality.

Losing heat or “sooting up” is not uncommon; let’s have a look at the possible causes…..

By far the most common is over fueling. Most of the time excessive soot becomes an issue after a service. Oil cookers use the wicks only to get going. After this the heat from the shells vaporises the oil as it arrives in the burner base. This vapour burns cleanly and relatively efficiently. Sometimes though after a service, when everything is newly cleaned, too much oil can arrive at the burner base even though the flow rate settings on the valve have not been changed. Of course if the valve has failed the same issue can present itself. When this happens the oil cannot vaporise fast enough and it begins to burn directly. This, as you can imagine, is inefficient, sooty and a messy business!

To solve this issue you'll need to get your engineer to adjust the flow rates on your control valve downwards. The original valves were made by BM, but these have now been superseded by a valve made by Toby. Whilst they are a like for like swap they do require calibration to the appliance.

clean and sooty flames

A similar issue is if the burner base has been re-installed lower after a service. The increased depth of the oil will again cause the oil to burn directly. You'll get a yellow flame - not a lovely efficient blue one! A yellow flame is a sooty flame and thus the burner base needs to be recommissioned and levelled again basically to solve this!

Aga perfect blue flame

After over fueling the next most common cause of a sooty and low temperature Aga range cooker is a change to the flue. Insufficient draw means the carbon that forms as an inevitable by-product of combustion does not form in the 'right' place. Your flue draw can change for many reasons even if you don’t change the length of it. Maybe a bird has disturbed or knocked a cowl off, maybe the tree you chopped down exposed the flue to more wind or maybe your neighbours conservatory has left it becalmed - all of these can ruin the careful balance in your range cooker and make your flue draw too high or too low. Too high and your range cooker will run cool and struggle to reach temperature, too low and it’ll ‘soot’ up quickly – it can be a difficult balance!

Gas fired Aga

Often engineers will blame ‘low sulphur’ fuel (cleaner fuels have been legislated for by governments to reduce carbon and air pollution!) but most range cookers have been running perfectly well on these lower sulphur fuels supplied by global refineries for over a decade. So before you start blaming fuel quality or trying expensive fuel additives and the like have a think about what, if anything, could have changed your flue conditions or have caused over fueling!

A key point to remember is “bad oil” cannot be chemically changed to “good oil” by adjusting the appliance that burns it, nor can it be substantially altered by putting a litre of expensive additive in 1000 litres of Kerosene. If the Aga is not working correctly before a visit by an experienced engineer, but properly afterwards, or alternatively was running perfectly well but then fails soon after a service then it is very clear that the cause of the problem was the appliance not the fuel or fuel supplier.

For everything you needed to know about oil fired boilers, oil tanks and heating oil deliveries, take a look at our FAQ’s and other news.

Plumbteam publish a vaporising burner servicing guide so that you can check that your engineer is doing his inside work properly. They fail to mention that inspecting the tank and tank filter is a job that your engineer should also perform at every service as poor tank condition and blocked filters can quickly impact on the fuel and the appliance burning it.

Oil Fired Aga Top removed

Their guide covers servicing a pot or vaporising burner, as found in AGA, Rayburn, and Stanley ranges, plus many others. Plumbteam Vaporising burner servicing guide.

Additionally the FPS & OFTEC Industry Briefing Note from 2009 on Appliance Combustion Issues provides some more information and background on carboning in vapourising burners.