First, we assume from your question that you have a two-handle faucet. When your hot water is running from both the hot and cold sides of your faucet it means that the rubber gaskets within the valves are leaking. It could be that only the hot side is bad, but we would recommend that you change both. The gaskets cost fewer than 50 cents, but can take quite a while to install. There is a diagram on our web site at that will help you through the process. Type "faucet repair" into our search engine. Select the first choice that comes up.