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Why is my diesel heater sooting up?

I have a Kabola Old English drip feed diesel room heater which has given me good service over 13 years. It only needs decoking two or three times each winter and normally burns with a nice blue 'cup' of flame, indicating (if I remember my school chemistry lessons) good combustion.
Just this winter it has started to get very sooty and yellow, and even two or three days of burning leaves an appalling amount of diesel-laden soot after I turn it off. And I seem to need to clean it almost every day.
I was wondering if there's something wrong with the burner, or am I encountering the new dreaded 'biodiesel'?

Asked by: Andrew Denny  | 7.48pm, Tuesday 31 January

WW says:

One of the first things that I would check is that the flue is clear and not coked-up. This would reduce the temperature ofthe flame by restricting air flow through the burner.
Also the regulator valve may be allowing too much fuel to flow, though this is less likely. Is the burner cup preheat tube, where the fuel enters, clean and free from carbon as well?
Biodiesel effectively burns at the same temperature as petroleum derived fuels- though generally cleaner! Plus the proportion in diesel fuel is fairly limited. These boilers happily run on a range of gas oil type fuels.
I will come back with a more definitive answer- but firstly check the flue!

Mark Langley  | 9.19PM, Tuesday 31 January

I assume that you have followed the procedures for a more deep clean, including removing the burner pot, cleaning the burner pot, between the two layers of the burner, and cleaned the catalyst pad. Making sure the burner holes are scraped out (such as with a thin metal ruler) should help with air getting in.
Another thing that might be a problem is the catalyst might have decomposed enough that it no longer allows the fuel to burn in a controlled way; the catalyst allows complete combustion without large air flow and at a lower temperature than would otherwise be required. If the mesh is clean and intact, it is unlikely that it needs replacing though.
As well as checking the chimney, you might also want to check the draught regulator is still able to open/close, and that the counterweight is set about right to prevent flaring, but isn't firmly sealed shut!
Checking the chimney is properly sealed might help- or at least, going over the existing joints carefully- this will also help minimise chances of CO poisoning!
Checking that the burner pot isn't damagedand the gasket around the base of the burner is intact would be a good point, to ensure that air is going where it should through the burner and the same for the door seal as well.
Failing all those points, you might have to see a Kabola specialist. They might insist on a proper height flue though, to help the burner run more efectively...

Mark Langley  | 9.41PM, Tuesday 31 January

Have you started to use any sort of fuel additives? Some of the additives that 'lock' any water in the fuel tank into the diesel to stop the dreaded 'diesel bug' have been known to cause problems with some diesel heaters. This is because a stove burns the fuel at lower temperatures than a diesel engine.
The other possibility is the mooring. Are you in a different location that does not give such a consistent draught up the chimney. The flue lengths are very short on narrowboats (often shorter than the manufacturers recommendations) and any down draughts or a poor 'draw' can affect the combustion.
Best of luck.

Rupert Smedley  | 11.20PM, Thursday 2 February

Readers say:

Had same problem . Not fully solved but...
1. The fire was flooding with fuel , which causes soot and soot build up in a big way !
2. Clean fire especially pot, making sure you clean underneath the lip useing a bent hacksaw blade (take the pin out of the blade end to stop it catching )
3. Fire will burn blue again unless it floods and burnes yellow and starts to block things up with soot again
4. Find out why it's flooding . Regulator ?!
Basically it's a problem (flooding ) causing a secondary problem (soot and soot build up)

Paul Horrocks  | 10.38PM, Monday 10 October

Little update.... the reason my old English was flooding and sooting up was this...
They work by getting the correct amount of fuel and air giving a blue ring with yellow flames (bluer the better) you should have none or very little smoke coming out of the flue when fully warmed up and always use with the door closed.
The reason for flooding and giving yellow flames and awful black soot everywhere was the regulator. Nothing wrong with it but it has a range of pilot -6 . Pretend the range is only pilot - 1.5 . bingo ! Seemingly these regulators are fitted to many different fires . The old English is small and dosnt require a lot of Diesel .

Paul Horrocks  | 11.16AM, Friday 14 October

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