I'm installing a new water heater. The cold water inlet is turned off and no water is running in the house.

After attaching the hot water outlet to the water heater I can hear water flowing/dribbling into the water heater.

Does this mean I have a bad valve that is allowing cold water to back-flow to my water heater? I can't hear water flowing at any of my sinks, tubs, etc. How could I find the bad valve.

Additional information: This has been running for over an hour and even with water heater off a small stream of cold water runs from all my faucets when I turn on the hot water side of the faucet.

  • it may be water in the pipes between the shutoff and your water heater. Does the dribbling stop after a while?
    – depperm
    Mar 24 '20 at 15:37
  • 1
    It sounds more like it's running than dribbling and it has been running for over an hour :( The weird thing is if I turn on water faucets in the house the hot water side still runs it just is a low stream. The water is cold coming out not hot Mar 24 '20 at 16:21
  • Have you only turned off the cold water supply on top of your water heater or have you turned off the main water supply valve on the main pipe coming in from the city ?
    – Alaska Man
    Mar 24 '20 at 17:02
  • 1
    Only turned off the cold water supply on top of the water heater Mar 24 '20 at 17:56
  • There's a lot of water in your pipes. Do you have a pressure tank attached? (blue). And do you know your valve is REALLY off? Is it a Gate valve or a 1/4 turn valve?
    – J.Hirsch
    Mar 24 '20 at 18:35

This is because after turning off your water you still have water in the pipes. The water heater in most houses is at one of the lowest points in the house. Meaning that even after turning off water at tap and even after leaving a faucet open, whatever is lowest will still get what water is left in the lines.

It is funny because my new helpers go through this exact experience when prepping for plumbing work. And they are each surprised about the amount of water that is still left in the pipes (and more surprised that they have to clean it up).

What you are experiencing is normal and if the water heater is the lowest (gravity) or one of the lowest spots in your water line it is perfectly normal to hear water flow after it is turned off and then dribble for a while - takes 5-10 mins for gravity to works its way out sometimes.

  • 2
    I agree I will usually open a hose bib out side and turn a faucet on to keep from making a mess when I replace a water heater , even in a single story ranch it is amazing how far the water will flow if the pipes are not drained.
    – Ed Beal
    Mar 24 '20 at 16:15
  • 1
    The CO did note it was all the faucets which would include the highest in elevation but I'm willing to bet that this is still the answer and either the CO might be slightly misspeaking, or might be coming from a shower that has higher plumping that a faucet.
    – Ack
    Mar 24 '20 at 18:34

As user Dmoore said, a lot of water left in the pipes could be flowing back to your hot water heater, but there is another possibility at play here: you have defective (worn) tap mixers that allow the water to flow from the cold to the hot.

In some places, I have seen homemade and commercial mixer taps where two valves control the hot and the cold water feed (some temperature setting), and the two outputs are connected through a tee to a third "flow" valve. In such a setup, having check valves would ensure that the water does not flow from the cold to the hot (and vice versa) when the "flow" valve is shut off but not the two "mix" valves. This would be especially bad if you had a high-flow appliance nearby such as a toilet as the toilet could be drawing some hot water through the mixer, via the cold water pipe. This situation can happen when undersized water pipes

It is not a bad idea to install a shutoff valve on both sides of the water tank to make replacement easier, without having to worry about the leftover water in the pipes flowing back to the water tank.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.