One of my husband's friends is having this problem. The kitchen sink has some sort of pipe that vents to the outside wall of the house. The sink is set up against this wall. The pipe on the outside of the house is dripping hot water, in a fairly steady stream. If any faucet in the house is turned on, the leak stops. My husband says the pipe does not seem to be directly attached to the hot water heater. I've never heard of this problem before. Any suggestions on what is the cause? What is the solution?

Hi Debbie,

It can only be from the T & P (Temperature and Pressure) valve from the heater. To check have him pull up on the lever and let some water out. Water should come shooting out if that's the case. One explanation might be a check valve or back flow preventer installed on the water service.
When new codes forced us to install check valves and backflow preventers on water service lines that made the water system a closed system. That meant that when the heated water expended it could no longer expand back along the water service line and would build up pressure in the syatem. This would kick off the T & P ,(Temperature and Pressure Relief) valve and the valve would discharge hot water out the relief line. To prevent this we installed a Expansion,(Air) tank on the heaters cold water supply line for some place for the water to expand to. It's either that or a faulty T & P valve.
Regards, Tom