Has any one out there suffered problems with their oil boiler after having a delivery of oil this year? I have! My ageing Grant boiler(boiler house version) which has a Riello burner started playing up shortly after taking delivery of 900l of new spec 28sec kerosene on top of 300l of last year's stuff. The boiler took multiple attempts to fire up when heat is called for. The boiler didn't go to lock out but just kept trying up to 6 times at about 15second intervals until it managed to stay alight. I had a service back in November and a new pump fitted. The combustion was tuned up at that stage and things were fine until the new oil arrived. I cleaned and adjusted the ignition points (they were a bit sooty) and swapped the control box with a spare but no improvement. The oil line filter is clear.  I then fitted a spare complete burner which had also been tuned up for use while the other burner was away for the pump fit back in November. This is displaying exactly the same symptoms with multiple attempts to start. I then realised that the new oil was at fault and decided to tinker with the air mix. During this process I found that the problem disappears if the burner is run without the cover on. Put the cover back on and it goes into repetitive start mode again. This implies that more air is required at the entry to the fan as the fitting of the cover obviously restricts the access of air compared to the cover off situation. I realise that I need to get my engineer in to re tune both burners but this goes against the grain a bit as I've already spent loads out on the boiler this year irrespective of the price hike in oil - 39p/l in August last year and 50p/l in early Feb this year! Any comments or similar experiences? Having taken the issue up with my oil supplier all they could suggest is selling me some additive concoction