Plumbing Leak At Water Heater Drain Line
We went to a customer's house yesterday because he had water coming from a pipe by his front door. He was calling it a plumbing leak, but if is coming from a pipe that is intentionally placed there, it is probably mechanical in nature. There are a few situations where you would see this. One is from the air conditioning condensation pan, and the other is from the temperature and pressure relief valve (TPR) of your water heater.
You typically would only see the a/c condensation drain line dripping if the a/c is running, and it is fairly humid outside.
I put my hand under the pipe and the water was hot, and so it narrowed it down to the TPR valve of the water heater. The water heater happened to be on the exact opposite side of the wall, so it was pretty obvious. The TPR valve opens if the pressure in the tank exceeds 150 psi or if the temperature in the tank is higher than 210 degrees.
Sometimes the TPR valve is bad and it needs to be replaced and at other times it is operating properly and doing its job to prevent an explosion. You can go inside the house and turn on a hot water faucet this will allow hot water to drain out of the tank and cold incoming water to cool the tank down. I would also check the thermostat's setting. You probably have room to turn it down, save some energy, and still maintain your comfort.
Some people will test the TPR valve by flipping up the tab on the end, and this is a good idea. However, many times the TPR won't stop leaking after toggling it. You can try a gentle tap with a hammer to see if this reseats it. If not, you may have to replace the TPR valve.