On monday i fitted a brand new burner £200.all new seals and gaskets and Ran for 2 hours from a jerry can of fesh fuel i noted how hot and how much quicker the system got to temperature once satisfied alls well, i reconnected back to the boat fuel supply and ran, initially all seemed well, just after 25 minutes the very feigntest of wispy smoke was witnessed from exhaust.....needless to say back on jerry can now. So, my conclusion is i may have poor fuel, but ive also learned, that its quite likely that combustion has never been 100%. Which has also been a factor.. webasto software downloaded now ☺ thanks for all the advise Chaps