Most flow problems can be fixed by simply running the lamp. The lamp can be put on a timer to run the lamp for you. Set the timer to run the lamp for 8 hours on (or as long as it can be run without overheating), and 8 hours off. Run this cycle until the flow improves. If the flow does not improve after a month, than there might be a more severe problem with the lamp.
Does the wax all rise to the top and never falls?
The most likely cause of this is that the lamp is too hot. If the lamp is too hot, the balance of the lamp may be off. Rebalancing the lamp is a very hard thing to do. If you do not know what you are doing, it is best to ask people before trying this method. What must be done is the correct amount of fluid must be taken out and replaced with distilled water to reduce the density of the liquid.
Does the wax never rise?
This is the opposite of the problem mentioned above, but it is much easier to fix. Increasing the density of the liquid is possible by adding pickling salt to the liquid. It is recommended to remove some fluid to premix the salt, and then pour that fluid back into the lamp until it flows. Another method is to remove some fluid and replace it with propylene glycol until it flows.