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Context. Class II methanol masers at 6.7 and 12.2 GHz occur close tohigh-mass young stellar objects (HMYSOs). When they are observedsimultaneously, such studies may contribute to refining the characterisation oflocal physical conditions.  Aims. We aim to search for the 12.2 GHz methanol emission in 6.7 GHz methanolmasers that might have gone undetected in previous surveys of northern skyHMYSOs, mainly due to their variability. Contemporaneous observations of bothtransitions are used to refine the flux density ratio and examine the physicalparameters.  Methods. We observed a sample of 153 sites of 6.7 GHz methanol maser emissionin the 12.2 GHz methanol line with the Torun 32 m radio telescope, using thenewly built X-band receiver.  Results. The 12.2 GHz methanol maser emission was detected in 36 HMYSOs, with4 of them detected for the first time. The 6.7 GHz to 12.2 GHz flux densityratio for spectral features of the contemporaneously observed sources has amedian value of 5.1, which is in agreement with earlier reports. The ratiodiffers significantly among the sources and for the periodic sourceG107.298+5.639 specifically, the ratio is weakly recurrent from cycle to cycle,but it generally reaches a minimum around the flare peak. This is consistentwith the stochastic maser process, where small variations in the physicalparameters along the maser path can significantly affect the ratio. Acomparison of our data with historical results (from about ten years ago)implies significant (> 50%) variability for about 47% and 14% at 12.2 GHz and6.7 GHz, respectively. This difference can be explained via the standard modelof methanol masers.

Observations of 12.2 GHz methanol masers towards northern high-mass protostellar objects