Stability and burnout natural-circulation tests on an electrically heated 7-rod cluster were carried out to obtain data relevant to the Halden II reactor. The object of the tests was to measure the maximum channel powers obtainable without burnout at pressures up to 28 atm and various inlet subcoolings. The test-section heat flux was essentially uniform, but local heat-flux peaks were introduced at hot patches to probe burnout. It was found that at 28 atm and up to 6°C inlet subcooling, a channel power of nearly 600 kW could be reached without burnout or instability; increasing the subcooling further, reduced the burnout power. The instability channel power threshold was investigated and found to decrease with decreasing pressure. In addition, the natural-circulation inlet velocity was measured at various constant pressures and values of inlet-subcooler heat removal, as a function of channel power up to and in the hydraulic instability region. Flow oscillations of about 1-sec period were observed and recorded together with the burnout detector signal at trip under these conditions.