From the FAQ at http://www.lavalites.com/LavaFAQ.html:
NO FLOW/LOW FLOW (aka the lava is not moving or the lava is sitting
at the bottom of the globe)
If the lamp has warmed up completely (the lava is melted and the lamp
has been on for at least four hours) and the lava either settles to
the bottom and stops flowing or the lava never flows at all, follow
the instructions below.
1) Remove the globe from the base and set it on a flat even surface.
(like Fig. 1; See the web page)
Be very careful as the lamp is hot. Use pot holders if necessary. Do
NOT shake the globe or turn it end over end as this will permanently
ruin the lamp and void your warranty.
2) Leave the flat bottom of the globe on the table. Grip the cap and
gently turn the globe for about a half minute so the lava rotates
around the metal coil inside the very bottom of the globe.(see Fig. 1)
2) Put the globe back on the base. The flow usually picks back up
again within an hour or so. Sometimes you will need to repeat the
process several times (or during the next time you run the lamp).
To which advice, I will add:
If you have a fake (not made by Haggerty or Mathmos), throw it
away and get the real thing. I have never seen a fake that
worked right.
Operate your lamp for no more than 8 hours at a time and for
no less than 2 hours at a time.
Keep your lamp's environment reasonably cool. If it feels
like the room is hot, don't run your lamp.
Use only 40 Watt appliance bulbs.
Operate your lamp with the plastic cap on.
--
Guy Macon
<http://www.GuyMacon.com/>