If your lava lamp has stopped flowing due to wax sitting at the top that never falls until the lamp cools off then your wax has separated into two different densities. This can be corrected by a fairly simple, but invasive process. This can happen due to lamps stored in high temperatures while unused. For example lava lamps stored in garages and attics. It can also happen over time with normal use in some cases. This method can also be utilized to fix wax that has become mottled in appearance. Sometimes you can gently swirl the lamp around to fix the wax or gently turn it end over end until it mixes again, but doing so can lead to the lamp being shaken up ruining the lamp entirely.
Typically it looks something like the two pictures below. Often times when the wax cools down it still remains in two separate chunks. This is not to be confused with a lamp that does flow, but the wax accumulated at the top, but eventually does fall. You just have an over heated lamp. Sometimes the wax can actually be stuck to the glass itself and it stays stuck to the glass when cooled. This method will not fix that. Wax stuck to the glass usually indicates the formula is breaking down and reaching the end of its life.
Step 1 involves letting the lamp completely cool to room temperature, removing the bottle cap from the globe, and pouring the master fluid into a clean jar. The two bunches of wax should now be sitting at the bottom of the globe. A Guide for removing the cap and recapping the lava lamp bottle can be found here.
Next place the globe in it’s lamp base and turn it on. It will melt much quicker than normal since there is no master fluid. Try not to let it overheat. You can remove it from the base once fully melted. If you are following this technique to remove mottling from wax you need to heat the wax until the mottling goes away. Gently swirl the wax around in the globe. A good 30-60 seconds should be enough. Make sure there is no chunks in the wax. If you see any clumps form then the wax wax not fully melted. After gently swirling let the wax fully cool to room temperature. This can take a couple of hours. It is best to have patience because the wax can appear cooled and hardened, but still be molten in the center.
Once you are certain your wax has fully cooled reintroduce the master fluid to the globe and then recap the lamp using a new bottle cap. Reusing the old bottle cap is not recommended because they rarely, if ever, provide an adequate seal to prevent leakage.
That’s it. Your lava lamp should run normally now!
The Lava Library 