When the vampires attack the monks who guard the special cross, the cross is found flanked by tall, burning candles. The next morning, as the hunters survey all the dead monks, they find the place where the cross once was. Those same candles are still burning and are still just as tall as they were the night before - no wax drippings either!
Candles in churches and the like are usually made of hollow plastic and burn off of paraffin that is stored inside. this means that they will be able to burn for a long time and will also remain the same length as the outside isn't melting.
ever heard of those everlasting candles that were in the catacombs and when you open the door to give the tomb new air, they suddenly lit up to give the appearance of burning for the whole time... they not ONLY had a material that burned when it hit the air and looked like a candle, but ALSO had a HUGE room behind it full of oil for the lamps to burn in case the material ever burned out.