  It is shown that thermal inflation arises naturally in rank greater than five
unified theories when non-renormalisable terms are introduced. Thermal
inflation is driven by two Higgs fields \Phi_{B-L} and \bar{\Phi}_{B-L} which
also break U(1)_{B-L} when acquiring vevs at the end of inflation. The
inflationary period provides enough e-foldings to solve the monopole problem
for M_{B-L} \geq 10^{12} GeV. We point out that observations suggest that
M_{B-L} \simeq 10^{14} GeV.
