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1 Airtonic D4 Burner cut open.
Derek's conclusions on burner.

We already knew that the louvres at the entry point of the blown combustion air delivered the air in a spiral or helix rotation, and suspected that there was a hidden secondary fuel screen to assist the air/fuel mix procedure. However, the photos have given a greater understanding of the entire combustion process.
They show a coarse steel mesh lining both inner and outer surfaces of the main combustion area. We already knew that fuel is pumped round the outer top edge of the glowpin screen, where most of it flows down the path of least resistance - the outer layers; then drops onto the combustion area mesh. Here it spreads around the mesh to vaporise and mix efficiently with the combustion air. But a small amount finds its way into the centre of the screen, where during the start-up procedure it is ignited by the glowpin. The flame then enters the main combustion area to ignite the rest. Once the chamber has heated up, the flame becomes self-sustaining, and the glowpin is switched off. It will only come on again when heater comes out of standby, or for 40 seconds after heater is switched off to clear any remaining fuel.
On the whole the burner is low maintenance, and rarely causes major problems so long as heater is correctly installed. It usually only needs cleaning during a normal service; and soaking it in a caustic soda solution, or other suitable cleaner should clear any carbon from the inaccessible area. Often only necessary if flame tube is heavily clogged.

Now the D4 burner itself. Roy could not have found a better specimen to examine.
In rare instances, poor installations,lack of servicing or simply very long use can cause catastrophic burner failure, as our autopsy page illustrates. We have to admit that we do not know which reason caused this one. All the heater components are manufactured to last for at least the design lifetime of the heater. This lifetime figure is not a fixed number of hours, it depends on how hard the heater works,  number of starts and a host of other factors. Heaters used on low heat last longer than ones running on high heat. After a very long hard life burners can eventually fail, this one was showing some signs of deterioration.
Used Airtronic D4 burner bought on ebay.
No reason was given why it was replaced.
Burner would have been cleaned before we bought it.
Externally it showed no visible sign of damage.
Until recently we had been unable to explain how an Airtronic burner can fail when it appears to be in excellent condition. We bought a used D4 burner on Ebay, advertised as working but with a low price so we guessed it was probably not much good. We must be the only buyers of something on Ebay advertised as working who were hoping it was actually faulty. Attacking it with a hacksaw revealed its internal condition was very poor and must be close to failure, but it was just what we wanted. We learnt more about failure mechanisms from it than we ever would from cutting up a new one. We have been told of one burner failure, not Airtronic, that was found to be clogged with sand after cleaning by sand blasting.
End view showing burner combustion air inlet and fuel pipe.
Air inlet cap removed, view of underside.
The retaining pins are soft and it levered off easily.
Spiral grooves cause the combustion air to spin into the burner.
Some carbon deposits here.
Possible indication of some localised overheating?
It will never work again.
Side 2.
Endcap replaced temporarily for photos.
Outer screen might have covered the glowpin screen but it partly disintegrated during cutting so we cannot be sure.
Side 1
Glowpin screen upper left is multi-layered, the cut reveals its thickness.
Side 1.
Different view.
Finally the shots that made the effort and cost worth while. Click on the images for larger pictures.
Click on images for larger pictures.
Burner sawn in half. Sawcut positioned to cut through the glowpin screen and fuel inlet.
Side 1.
A very coarse inner mesh is visible through the central slot.
Side 1
Loose wire strands were caused by hacksawing.
Side 2.
Disintegrating mesh and extremely solid carbon deposits. It also shows why mechanical cleaning cannot clean the insides of the burner. This burner was probably already starting to fail which explains why it was sold.
Eberspacher Burners revealed.
2 Airtonic D4 Burner fixed.
Mike diagnosed a fault on his ebay purchased Airtronic D4 to a faulty burner.
For most users chemical cleaning clears the burner but in this case two types of cleaner did not remove the deposits so Mike had to be more drastic.
The majority of our users including ourselves would not have the welding facilities to fix by this method.

Burner tube cut with an hacksaw to get at hidden parts. It was clogged with very hard carbon.
Some deposits could be chipped out.
The remaining deposits were removed using a blowtorch,  heating and cooling several times to soften and break them up.
Cleaned burner inside. One interesting feature is that unlike the D4 burner I cut apart there is only the outer mesh with no central mesh.
After welding back together the burner worked ok.
Visible parts of the burner were clean.
D4 burner from an 02 03 04 model.
A burner from a D1L. Damage to the main burner parts was not caused by dismantling.
The part on the extreme left had to be separated from the burner to remove the burner.
We have no idea why this has happened but D1L are very old heaters.
More detail of the above burner.
The metal has been burnt through.
D1L Heat exchanger which contained the faulty burner. Upper left is where the part with the fuel pipe fitted. That joint would have had to be broken to remove the burner. Picture shows the area behind the burner that is normally hidden and cannot be accessed for mechanical cleaning.
3  D1L Burner failure.
Fuel is delivered to the burner from the fuel pump and is mixed with pumped air from the blower. Initially the glowpin provides the heat to ignite the mixture. Once the burner gets hot enough the flame becomes self sustaining and the glowpin is switched off.
A chemical clean of the burner together with new glowpin screen (modern heaters only), usually cures most problems. On older heaters the glowpin screen is fixed and is not replaceable.
Serious burner failures are rare but they do occur.
All the information we have on serious burner failures is on this page.