The KATRIN experiment measures the electron antineutrino mass with a sensitivity of 0.2eV/c2. This goal sets strong requirements on the systematic uncertainties of the measurement. One main systematic uncertainty is related to the stability of operational parameters of the Windowless Gaseous Tritium Source (WGTS). These have to be monitored and controlled on the per mille level. To achieve the temperature stability of one per mille at the two operational temperatures 30K and 100K, a novel cooling system with liquid noble gases was developed by the KATRIN collaboration. The poster reports of the first tests of the WGTS cooling system during the last year, which demonstrated the outstanding performance of the cryostat with a temperature stability being one order of magnitude better than envisaged. The same was demonstrated for the magnetic field stability of the seven superconducting magnets of the WGTS with field strengths up to 3.9T.