The small pipe ends on the outside wall next to them outdoor faucet. Water is constantly dripping but isn't warm/hot. Recently had a plumber install expansion tank hoping that the problem would be solved. The tank is installed horizontally. Water is still dripping. Plumber thinks the drip isn't related to water heater.

Can you please help me diagnose what is causing this water drip?

water dripping

expansion tank installed

  • 2
    How long has this been happening? What is the weather? What’s in the other side of that exterior wall? Why did you suspect the hot water heater? Apr 23, 2023 at 13:03
  • 1
    Have you tracked it. Is it an overflow from your toilet cistern? It could be from a pressure relief valve from the cylinder. Depending on far the water has to travel, it may cool down a bit. Apr 23, 2023 at 13:43
  • @JacobKrall it's close to a year now. :-( garage on the other side, with water heater. My preliminary Google search told me it's the water heater, and so is a neighbor who got it resolved for him with an expansion tank install. so I tried the expansion tank. It's been the same on freezing cold days and boiling hot days as well.
    – Arun
    Apr 23, 2023 at 14:29
  • If it does come from the water heater, it is mostly the drain for the pressure relief valve. If so that valve is leaking and needs to be repaired or replaced.
    – crip659
    Apr 23, 2023 at 15:54
  • 4
    A picture of where the pipe originates might be helpful.
    – HoneyDo
    Apr 23, 2023 at 15:56

1 Answer 1


My first guess is that it’s a condensate drain line for your air conditioner. Second guess is a dehumidifier drain. Third guess (thanks to @crip659) is a broken pressure valve on the hot water heater.

  • Pressure release valves, in my experience, are easy to open, but not so easy to get them to close again. They sometimes seem like single-use valves! You may need to replace this valve. To see if this is the problem, turn off the water and the water heater. This can leak even if the water is shut off, as the heating water can expand and overflow even if there’s no mains water pressure.

If that’s not it, shut off the main water to the house, and see if it keeps dripping.

  • If it does, the water is coming from the air, not the pipes. Shut off each circuit breaker, check if the water is still leaking. That should narrow it down to one appliance.
  • If it stops, it’s a plumbing leak. Try to follow the pipe to figure out where it’s connected on the other end.
  • 2
    The problem with relief valves is that when they do open there is a good chance of getting sediment struck in their seat. Most times they just need a good rinse when open.
    – crip659
    Apr 23, 2023 at 16:59

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