Waterbed specialists Land and Sky recommend a temperature of 85 degrees Fahrenheit to begin warming a waterbed, gradually adjusting the warmth until it reaches a comfortable level. It takes 24 to 48 hours for the bed to fully warm.
During the initial warming phase, additional blankets help to retain the heat. Thereafter, it is important to keep the bed covered. Proper placement of the sensor between the mattress and the liner ensures that the heating unit does not run all the time. If the bed is not heating enough, the sensor may be too close to the heating pad, and readjustment is advised.