Truma Combi 4 E Strip down & replace heating elements

Discussion in 'Heating and Air-Conditioning' started by Abacist, Apr 16, 2018.

  1. Abacist

    Abacist Funster Life Member

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    My boiler does not heat water using the electricity. As far as I can tell there are various warning lights to indicate most problems but indicate that the heating elements are kaput other than the fact that everything looks normal at the controls but the water just refuses to heat.

    Before starting to work on the boiler, for safety, I turned off the mains electric hookup, switched off the 12 volt power system and turned the gas off at the gas bottles in the gas locker. The van has not been used for a couple of months.

    I have checked the obvious things like live power to the boiler, fuses not blown etc but nothing. I haven't found any videos or pictures of how to do it so I'm going to take you through my attempt to replace the heating elements which are currently on order at the extortionate price of £309!

    You have to access both ends of the boiler so it probably needs to be removed from your van and put on a bench. To achieve this you need to disconnect both the mains and 12 volt electric cables. I have taken a photo of the 12 volt connections so that I can put them back in the right places on the printed circuit board. There are 4 hot air tubes to be removed which are held in by 4 philips headed screws. There are hot and cold water connectors to be removed so make sure that you have emptied all the water from the van and boiler before removing these. The gas connection needs to be removed which needs a 17mm spanner. The exhaust pipe has an outer sleeve which needs to be removed which again needs a philips screwdriver. Inside there is the exhaust pipe with a clamp that on my Autotrail Savannah 2010 has a star drive screw. There are 4 large philips screws holding the boiler to the floor.

    You can then lift the boiler out and as its made mostly of aluminium its not too heavy. I rested mine on a garden bench with the water outlets downwards to let out the remaining water.

    Here its is now on the dining room table ready for dismantling though the electric overs have already been removed. The top 12 volt cover just unclips. The 230 volt cover needs to have 2 star drive screws removed at top left and top right. I have also removed a cooling fan cover which just unclips and slides up.

    Photos to follow shortly!
     
    Last edited: Apr 16, 2018
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  2. Abacist

    Abacist Funster Life Member

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    IMG_3454.jpg IMG_3455.jpg IMG_3456.jpg IMG_3458.jpg IMG_3453.jpg IMG_3454.jpg IMG_3455.jpg IMG_3458.jpg
     
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  3. Abacist

    Abacist Funster Life Member

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  4. Abacist

    Abacist Funster Life Member

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    Now we need to take the cover off the other, left hand end when looking at the Electrical Printed Circuit Boards. These have star drive headed screws.

    The next picture shows that the outer cover has been removed to reveal an further, inner cover which needs to be removed.


    The inner plastic cover now removed and the 4 wires removed from the ends of the heating elements which are held on with 7mm nuts with 2 star locking washers either side of the electrical connector.

     
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  5. rosalan

    rosalan Funster

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    Don't stop now! I have just mentally dissembled our heater unit, although there is nothing wrong, as I cannot resist following demonstrations.
     
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  6. Abacist

    Abacist Funster Life Member

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    In theory with both ends of the heating elements now revealed and disconnected we should be able to remove them by pulling them out from the U shaped end but they are rock solid and won't move! On the end with the 4 heating element electrical connections I next removed the 4 rust coloured oval shaped grommets and then removed the aluminium cover plate. This needs to be teased away carefully as there is a rubber gasket holding it in place even after the screws have been removed.


    Just as a point of interest the hole in the middle is the gas boiler combustion chamber and contains a stainless steel sleeve.


    As a further point of interest here is the gas burner with its lighting electrodes

     
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  7. Abacist

    Abacist Funster Life Member

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    So we are now fully dismantled far enough to remove the elements.

    The following picture shows the ends of the heating elements and there is a free length of each element not between the fins of the heat transfer unit. My only choice is to drift these out gently using a wooden or rubber mallet choosing one element first and alternatively tapping each side to gently knock it out at the other end of the boiler. That's as far as I've got tonight so I'll carry on when I can tomorrow or later.



    The next three attempt to show progress drifting out the elements

    IMG_3467.jpg IMG_3468.jpg IMG_3469.jpg
     
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  8. Mr B

    Mr B Funster

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    Great thread. Really informative.....
    Now I know where the reset button is.....;)
    Thanks
     
  9. Abacist

    Abacist Funster Life Member

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    Yes the real problem with the reset button is that it is not visible until you remove the 2 screws for the main cover to the electrics and then you realize that there is a sleeve in the plastic cover which you could poke a screwdriver down to press the rest button! It must pop out when it needs resetting. I initially thought "red button" - I haven't got one of those until I found it when I took the cover off.
     
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  10. Abacist

    Abacist Funster Life Member

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    I should have mentioned this at the start but you ought to test your heating elements with a multimeter first to establish if they have failed. A heating element should have a resistance if it is OK. Here is how to calculate what the resistance should be and how to do the test.

    https://www.wikihow.com/Test-a-Heating-Element

    Mine both have no resistance whatsoever!

    However as can be seen you have to get a long way before being able to test the resistance of your heating elements!
     
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  11. dave newell lvs

    dave newell lvs Trader-Vehicle Services

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    Don't forget to use new rubber gaskets and seals on the burner assembly when you rebuild it. When the elements fail they often split and swell (which is usually what makes them difficult to extract. This also spreads the sections of the heat exchanger where they fit, you need to remove the heat exchanger and gently squeeze these sections to close them up, there is a specific dimension for the gap, Ill see if I can find it for you. If you don't do this then the new elements will not make proper contact with thew heat exchanger meaning performance will be poor and also that the new elements can overheat and fail prematurely.

    D.
     
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  12. Abacist

    Abacist Funster Life Member

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    So I've now drifted out both heating elements and it was not an easy job. Both were stiff inside the tube drilled into the fins. Don't set about this unless you have something small enough and which won't damage the tube in which the heating elements are located. I was fortunate to have both a long and a short 1/4 inch drive socket set extension bar which combined gave me just enough length to drift them out. The long one is 9 inches long and the short one 4 inches giving 13 inches total length.

    Here are pictures of the extension bars at the heating elements now removed which are 15 inches long and I could pull out the last three inches or so.

    Clearly the heating elements need to be a tight fit inside the fins to enable the heat transfer but I have to say that I am concerned at how I am going to get my expensive new heating elements back into the boiler when they arrive given the efforts with the mallet to get them out!

    IMG_3470.jpg IMG_3471.jpg
     
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  13. Abacist

    Abacist Funster Life Member

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    Thank you very much Dave. I am fortunate that I don't have split elements and apart from some light corrosion/rust on the elements they look in pretty good nick considering they have both failed.
     
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  14. Abacist

    Abacist Funster Life Member

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    So the new heating elements arrived along with a comprehensive gasket set and 2 packets comprising a complete new set of nuts, screws, bolts and washers. Attempting to fit the new elements and one pushed in with some slight resistance but the other one would not go in and I decided that it should not be drifted back in having seen Dave Newell's helpful post above. So some further dismantling required to remove the stainless steel hot water tank from the heat exchanger fins to expose them and adjust their tightness to allow the new heating element to be fitted. This is just a question of undoing the nuts which hold the boiler tank to the heat exchanger. When you think you've done this and expect the tank to come off it still won't budge so I felt all around the edge of the tank checking it was free or maybe stuck by another gasket but no there was a tight spot at the top. You then realise that there is an aluminium insert where the mini fan housing was located. Removing this exposes the last nut holding the boiler tank in place. Remove the tank and then the heat exchanger fins are exposed and can be adjusted in or out so that the new heating element can be inserted. Some more pictures follow.
     
  15. Abacist

    Abacist Funster Life Member

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  16. jezport

    jezport Funster

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    Rather than drifting the elements out how about putting a broad webbing strap through the loop end and pulling out?
     
  17. Abacist

    Abacist Funster Life Member

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  18. Abacist

    Abacist Funster Life Member

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    With hindsight I would have removed the stainless steel water tank from the heat exchanger which I ended up having to do anyway, adjusting the aluminium fins to enable removal and re-fitting of the new heating elements.
     
  19. Abacist

    Abacist Funster Life Member

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    Its then a question of refitting everything back onto the boiler in the same way as you took it off. Hopefully this thread will help others.

    My boiler is now ready to refit into the van and then I can reconnect the cold and hot water pipes, gas, electrics and air tubes ready for refilling with water and testing.
     
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  20. Lenny HB

    Lenny HB Funster

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    Great thread thanks for all the info. Are you going to put the info in the resources section?

    It has convinced me I have made the right decision with all 3 vans I've had by just having the gas only Truma. :D
     
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