I have a Gazco VFC Convector fire 18 " with control valve running on 2 x 12.5 kgs gas bottles. The fire goes out after approx. 4 hours use when the bottles are 1/2 to 1/4 full. We have had a chimney spill test which seems o.k. and cleaned round the pilot. Any suggestions?

Thomas Joseph Neilson, February 2010