JCMT spectra of the massive hot cores G31.41+0.31, G24.75, NGC 7538 IRS1 and W3(H₂O). The 229 310 and 229 452 MHz transitions in the lower sideband are indicated in red and that at 236 408 MHz in the upper sideband in blue. In green is the baseline, obtained by fitting line free portions of the spectrum. In all spectra the H₂CS 7₁ → 6₁ transition at 236 726 MHz is fitted to determine the typical linewidth in the sources, as listed in Table 1.