Stove was bought new (Hytta.de) in 2009. Was in storage until 2016. From then it is only used about 1/2 dozen times a year - faultlessly. This year issues with both burners. After a while, there is a "pop", the flame from the cap "deflates" and roars under the cap (glows red), there is a small yellow flame from the jet. I have researched this site and others: Can't believe the vapour tubes are clogged with carbon after 5 years and 30 fire-ups. Fuel is paraffin & supposed to be best quality (from Base Camp I think). Pricking / cleaning jet has no effect. There is no appreciable surging that I can see. Happens when tank under high or low pressure. As it's virtually a new stove, jets are still as Optimus fitted (and worked perfectly for 4 years) Any advice, please?