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Robbie's Guide To FBH Servicing & Repair
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Robbie
 


Member Since: 05 Feb 2006
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Robbie's Guide To FBH Servicing & Repair

1. Following (repeated) requests my (belated) guide on servicing the Fuel Burning Heater - as fitted to the cold climate RRS, D3 & D4 diesels. This guide is a follow-on from my guide to FBH Diagnostics posted here:

http://www.disco4.com/forum/topic123417.html

Click image to enlarge


2. The FBH reliability has become rather notorious and is often a source of frustration when the colder weather arrives. In truth this is somewhat unfair as the Webasto unit is a high quality bit of kit that sits unloved and unused under the bonnet for many months of the year before being asked to provide 5kw of heat. It does this without any scheduled servicing for years on end until it slowly suffocates itself with diesel combustion products. If serviced properly the FBH can provide many more years of happy burning.

3. The forum wiki provides a good description of the FBH, its functions, diagnostics and modifications. The unit itself is incredibly simple in operation - a fan draws air through the unit, fuel is fed to a small metal cup which is then heated by a glowplug and/or self-sustaining combustion. The burning gasses flow down and then escape upwards through the heat exchanger to the exhaust pipe. The heat exchanger is surrounded by a jacket of coolant pumped in and out of the unit:

Click image to enlarge


4. Once free of the supporting brackets the FBH comprises 5 main modules - The fan control unit, heat exchanger, burner, coolant pump and exhaust. So if you can count to 5 and work a spanner, screwdrivers and pair of pliers this is a job you can do yourself:

Click image to enlarge


5. Removing the FBH from the vehicle is pretty easy and self-evident. Remove the FBH fuse to remove power from the unit and its dedicated fuel pump; remove the electrical connectors, the fuel supply pipe and the 2 coolant pipes. As the FBH is mounted high in the engine bay you will not have a flood of coolant but please catch any spillage as the coolant is poisonous and attractive to animals. Removing the left headlight can make the job a little easier too.

6. Personal preference will dictate if you remove the unit complete with the silver mounting bracket and the exhaust, but I have a slight preference for unscrewing the unit from the silver bracket and disconnecting the convoluted exhaust hose so that they remain with the vehicle. For this guide the unit has been removed as a complete unit so that all aspects can be visualised.

Click image to enlarge


6. If the vehicle is required for use whilst the FBH is being serviced, or you would like plenty time to tackle the FBH, then the vehicle can be driven without the FBH fitted. Lines and fixtures should be secured / tiewrapped, open electrical connectors bagged and the open end of the fuel pipe plugged (no fuel will be pumped without the FBH fitted). The 2 open coolant pipes will need to be joined to restore the coolant loop. This requires a 20mm barbed plastic pipe connector which are about £2 to £3 for either a straight or right angled fitting:



7. There will not be much air in the system but a quick bleed of the coolant system via both bleed ports never hurts.

8. Tools required include T20, T25 & T30 torx screwdrivers, a pair of pliers and a 10mm spanner. Whilst not essential an impact driver and a pair of hose pliers does make the job a little easier:

Click image to enlarge


9. Once out of the vehicle the servicing can begin (shown here with the silver bracket and exhaust still fitted) by removing all remaining electrical connectors and fuel pipe (if still fitted):

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10. The 10mm spanner or socket is required to remove the exhaust; first at the bottom of the bracket:

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11. Second from the silencer:

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12. And finally the bolt at the convoluted tube clamp:

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13. The silver bracket can then be removed - it is secured by 3 torx screws:

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14. To reveal this:

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15. As the coolant pump covers some of the fasteners for the black bracket it has to be removed. It is secured by a metal clamp secured by a single screw. The short length of pipe linking the pump to the FBH can either be removed from the stub pipe or, as the stub pipes will be removed later, can be left plumbed in:

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16. With the pump removed the bracket torx fasteners can be removed:

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17. To leave you with the FBH itself:

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18. The 2 stub pipes are retained by an aluminium bracket, secured by a single screw. The pipes index against a small lug so once the screw is removed they are free to rotate:

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19. Behind the stub pipes there are 2 o-rings. These need to be removed and inspected:

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20. The black plastic cover can now be removed. It is held in place by 2 clips on either side at the top and a single large lug at the bottom. Pop the top clips first before swinging the cover away from the bottom tab, to leave you with the fan control module and heat exchanger:

Click image to enlarge


21. The heat exchanger/burner assembly is screwed to the fan control unit by 3 long torx screws:

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22. A small tap or gentle levering with a flat screwdriver should separate the 2 halves:

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23. The next bit is rather messy, so have a suitable surface ready:

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24. Once the burner has been pulled out (it may be stuck to the gasket, but it will peel away) it is pretty clear how the carbon deposits can slowly choke the FBH to the point that it cannot burn correctly or at all:

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25. With no plastics, rubber or internal sensors to worry about you can pick your favourite cleaning technique. Carb cleaner, brake cleaner and plastic scrapers can all help here, as does leaving it to soak overnight:

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26. The rest I cleaned with a very fine (blue) grade of scotch brite:

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27. That is it - your FBH is now clean and ready to run efficiently and cleanly again.

28. Assembly is genuinely the reversal of the above, but pay notice to the orientation of the gasket:

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29. …and the burner:

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30. Also remember to lubricate the o-rings with coolant or silicone spray to avoid leaks:

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31. Hopefully the assembled unit should look something like this:

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32. Hope this helps and if you have your own top-tips or suggestions please add them to the thread.

Regards to all.

Thumbs Up

This guide was brought to you by:

- RandomKamikaze who donated the FBH.
- Big Dave who provided free carriage.

Cool
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Last edited by Robbie on 3rd Nov 2015 6:42 pm. Edited 4 times in total 
Post #15553863rd Nov 2015 4:36 pm
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Robbie
 


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Robbie's Guide To The FBH Venturi Burner Assembly

1. This additional section deals with the more 'advanced' servicing of the glowplug and venture burner assembly, once it is removed as a complete unit in the guide above. Whilst I say 'advanced' the disassembly of the burner it is not particularly difficult; but disassembly is not usually required and, given the fragility of the gaskets, it is more likely that you will need some service parts to hand.

Click image to enlarge


2. Having disassembled the FBH to the stage above, including cleaning the exterior of the burner unit, you can inspect, service and/or repair the fuel delivery pipe, glow plug and the gaskets. The venture assembly is clamped down by a sprung top plate secured to 2 supports via those fiddly one-way round clips. No doubt people have their favourite way of removing these in an effort to avoid replacing them but I find gently rotating them with pliers can often lift them a notch or 2 which makes getting a pick under the 4 segments a little easier. With patience they can be worked upwards and off the retaining shafts:

Click image to enlarge


3. The glowplug is simply slotted through a hole in the ceramic part of the burner and is held in place by a spring clip that hooks over the top of the plug and slides between groves either side of the ceramic core. Pry the spring free from the side groves with a pick, small screwdriver or small pliers before lifting it free:

Click image to enlarge


4. With the spring and top plate removed the glowplug can be slipped out to leave the assembly like this:

Click image to enlarge


5. The plug and fuel delivery pipe will look like this (see, I said it was a rather simple design):

Click image to enlarge


6. The ceramic part of the burner can then be carefully lifted free off the 2 supports. There are a number of gaskets underneath and these are thin and fragile. I make no effort to remove them unless I have spares to hand:

Click image to enlarge


7. With the ceramic top removed the burner can will look like this, probably with a gasket or 2 stuck to it:

Click image to enlarge


8. The gaskets themselves really are very thin and once baked by heat they don't take kindly to being manhandled:

Click image to enlarge


9. It is worth inspecting the top aperture with the aid of a torch. Hopefully in the photo below you will be able to see the little metal cup that collects the fuel from above. As part of the start sequence this tiny cup of diesel is heated by the glowplug mounted in the glowplug aperture until the unit becomes self-sustaining. At this stage the glowplug turns off and is then used as flame-detector. As it is a non-ohmic conductor its change in resistance is proportional to the heat applied and this resistance is monitored by the FBH control boards. Unfortunately it is possible for the metal cup to perish or even fall free from its support. Clearly the FBH will not work without the fuel cup in good condition:

Click image to enlarge


10. Any excessive carbon deposits can be removed with carb cleaner and agitation with a soft brush. Pay attention to the fuel delivery orifice and a burst of carb cleaner through the pipe can help remove any gummed-up fuel. Please remember to lower your safety specs from their perch on the top of your head so that they actually cover your eyes, before squirting carb cleaner through small holes:

Click image to enlarge


11. Once cleaned and inspected the unit is assembled in the reverse of the above. My only top-tip is with reinstalling the little sprung hats on the 2 shafts. To apply an even and secure amount of tension they should be pushed down with something cylindrical that mates against the outer rim. A standard 1/4" hex bit adapter is just the right size, but a deep socket or similar will also do just fine:

Click image to enlarge


12. Again, feel free to add your own top-tips, experience and photos to the thread.

Regards to all,

Robbie
 Land Rover - Turning Drivers into Mechanics Since 1948

Battery & Quiescent Current Drain Testing

Diagnostics for:
Defender, FL2, D3, D4, Evoque, RRS & FFRR
A not-for-profit enterprise


 


Last edited by Robbie on 22nd Nov 2015 3:58 pm. Edited 1 time in total 
Post #15553873rd Nov 2015 4:37 pm
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focus340
 


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Brilliant!!

And surprisingly simple! Thumbs Up

Thank you.
 Ted



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Post #15553953rd Nov 2015 4:48 pm
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Martin
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Lovely write up Bow down

My addition would be regarding the coolant in/out stubs - mark the orientation before disassembly and make sure they go back together pointing the right directions. Saves a bit of swearing later Embarassed
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Post #15553963rd Nov 2015 4:49 pm
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geoffsnook
 


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Are the gaskets able to be reused or are they new gaskets if new how do you get hold of them please Thumbs Up
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Post #15554103rd Nov 2015 5:17 pm
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Martin
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The main gasket and 2 O-rings are available from LR as part number LR004141 for about £5
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Post #15554143rd Nov 2015 5:26 pm
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geoffsnook
 


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Thanks Martin for that i will order them just in case Thumbs Up
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Post #15554193rd Nov 2015 5:30 pm
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DG
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That's a wonderful guide there Rob ...you should be proud. Bow down Thumbs Up
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Last edited by DG on 4th Nov 2015 8:54 pm. Edited 1 time in total 
Post #15554203rd Nov 2015 5:34 pm
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radders89
 


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Top work fella. Especially love the image at No.8 where all the markings on the tools are facing you. Thumbs Up
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Post #15554603rd Nov 2015 6:09 pm
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ruben
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Robbie !!
Bow down Bow down Bow down Bow down Bow down Bow down Bow down Bow down Bow down Bow down Bow down Bow down Bow down Bow down Bow down Bow down


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Post #15554693rd Nov 2015 6:18 pm
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Aerialmark
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Hell that is a talent Robbie Bow down You could put Haynes out of business. So clear and concise even for a thicko like me. Well done Thumbs Up
  
Post #15554763rd Nov 2015 6:25 pm
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Robbie
 


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Martin wrote:
Lovely write up Bow down

My addition would be regarding the coolant in/out stubs - mark the orientation before disassembly and make sure they go back together pointing the right directions. Saves a bit of swearing later Embarassed


Yep, good idea. It is no particular drama if you get it wrong though, just loosen the screw and the stub pipes will ratchet around. This can be done with the FBH reinstalled too, albeit with a small leak of coolant.

Thumbs Up
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Battery & Quiescent Current Drain Testing

Diagnostics for:
Defender, FL2, D3, D4, Evoque, RRS & FFRR
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Post #15555483rd Nov 2015 8:15 pm
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tayaste
 


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You're raising the benchmark for 'How to's' , Really clear and simple .... Brilliant, Thank you Bow down
   
Post #15555523rd Nov 2015 8:24 pm
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Bodsy
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Great work Robbie. Thumbs Up Thumbs Up Thumbs Up
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Post #15555593rd Nov 2015 8:32 pm
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DiscoJake
 


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Ditto above, really raised the bar with that guide sir Thumbs Up

Quick question; when you disconnect the water hoses to remove FBH do you loose much coolant? Does it need plugging if the car's not moving or is it just a negligible loss from just the loop in the pump?

Bow down Bow down Bow down
  
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