End view showing burner combustion air inlet and fuel pipe.
Spiral grooves cause the combustion air to spin into the burner.
It will never work again.
Finally the shots that made the effort worth while. Click on the images for larger pictures
Burner sawn in half. Sawcut positioned to cut through the glowpin screen and fuel inlet.
Eberspacher Burners revealed
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 new glowpin screen and a chemical clean of the burner during a service usually clears most burner problems. On older heaters the glowpin screen is fixed to the burner and is not replaceable. Serious burner failures are rare but they do occur.
There are videos on youtube showing burners operating outside of the heat exchanger which may be of interest to some users.
Airtronic D4 Burner cut open
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 might 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.
Click on images for larger pictures
Another Airtronic D4 Burner fixed by user
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 decided to be more drastic and cut it open.
A Russian video on youtube https://www.youtube.com/watch?v=S9rMigqr0kM shows a similar repair to a D2 burner.
The majority of our users including ourselves would not have the welding facilities to fix by this method but could be done by a garage mechanic.
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.
Visible parts of the burner were clean.
D4 burner from an 02 03 04 model.
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
Used Airtronic D4 burner bought on Ebay.
Newer D4 burners have a different shape and are shown lower down the page.
Burner had been cleaned before we bought it. Externally it showed no visible sign of damage.
No reason was given why it was replaced.
Air inlet cap removed, view of underside.
The retaining pins are soft and it levered off easily.
Some carbon deposits here. Possible indication of some localised overheating?
Loose wire strands were caused by hacksawing.
Glowpin screen upper left is multi-layered, cutting through showed that thickness.
A very coarse inner mesh is visible through the central slot.
Disintegrating mesh and extremely solid carbon deposits. It also shows why mechanical cleaning cannot clean the insides of the burner. This burner was possibly already starting to fail which could explain why it was sold on Ebay.
Endcap replaced temporarily for photos.
The mesh has disintegrated around the hole in the mesh for the fuel input and glowpin,
Derek's conclusions on the D4 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. The photos have given a greater understanding of the combustion process.
They show a steel mesh lining the main combustion area. Fuel is pumped round the glowpin screen and then flows into the combustion area. Here it spreads around the mesh to vaporise and mix efficiently with the combustion air. During the start-up procedure fuel 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. (Updated information see Re-designed burner section below)
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 mostly 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 signs of deterioration.
Cleaned burner inside. Unlike the D4 burner I cut apart he found only the outer mesh. After welding back together the burner worked ok but it would obviously have been better to replace the mesh if a source of new ones could be found as shown earlier on this page.
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.
Leo bought an Airtronic D4 in 2001 in Sweden. The original burner would soot up if run on low heat for too long and after less than a year could not be successfully cleaned so had to be replaced. He told us the new re-designed replacement burner runs hotter and does not have that problem. It has the tube connected to the flange via an extended path so that it does not cool as much from the mounting flange.
Thanks for that information, we knew there had been a design change to the D4 burner but not the reason why it had changed.
Images from a youtube video
https://www.youtube.com/watch?v=S9rMigqr0kM showing a new D2 mesh.
D2 burner refurbish, replacing the mesh.
Eberspacher UK are not aware of a source of the new mesh.