When filling your waterbed many people want to speed up the heating process by adding warm or hot water. Of course with your drain and fill kit, filling the waterbed from the bathroom or kitchen sink is possible. So to answer the question is it ok to fill the bed with straight hot water? The answer is no. Filling a water bed with straight hot water can damage the vinyl. It is also possible to damage the heater. There is an over limit switch much like a circuit breaker that can trip which cannot be reset.
Do not plug in your waterbed heater until the mattress is full.
It is best to fill with a mixture of cold and hot water. Carefully test the water with your hand, and then the back of your hand where you are more sensitive to temperature. Getting the best temperature on a waterbed to your is like getting the perfect temperature for a baby bottle. If it’s hot its hot, if it’s cold it’s cold, simply regulate the water and make your temp. adjustment. It is likely that your hot water heater will run out of hot water while filling the waterbed. If it does, turn off both the cold and hot water and wait approximately ½ hour for it to recover and then turn on the water again.
Once the waterbed bladder is at the correct fill level, shut off the water, add your waterbed conditioner, and the burp the waterbed. It can take a waterbed heater up to a week to heat a water bed when filling it with only cold water, so we highly recommend mixing the hot and cold water to speed up the warming process and to make the mattress more comfy for the first few nights.