  We present MERLIN observations of OH, water and methanol masers towards the
young high mass stellar object IRAS 20126+4104. Emission from the 1665-MHz OH,
22-GHz H_2O and 6.7-GHz CH_3OH masers is detected and all originates very close
to the central source. The OH and methanol masers appear to trace part of the
circumstellar disk around the central source. The positions and velocities of
the OH and methanol masers are consistent with Keplerian rotation around a
central mass of ~ 5 Msun. The water masers are offset from the OH and methanol
masers and have significantly changed since they were last observed, but still
appear to be associated to the outflow from the source. All the OH masers
components are circularly polarised, in some cases reaching 100 percent while
some OH components also have linear polarisation. We identify one Zeeman pair
of OH masers and the splitting of this pair indicates a magnetic field of
strength ~ 11 mG within ~ 0.5" (850 AU) of the central source. The OH and
methanol maser emission suggest that the disk material is dense, n > 10^6
cm^-3, and warm, T > 125 K and the high abundance of methanol required by the
maser emission is consistent with the evaporation of the mantles on dust grains
in the disk as a result of heating or shocking of the disk material
