During this weekend, my water heater broke. I shut off the main water supply which stopped the water pouring out of water heater. It went to slow dripping with the residual water.

I shut off the valve to the broken water heater and turned on the main water supply. This had the effect of water immediately rushing out of the water heater forcing me to shut off the main water supply. I have two water heaters and they are supplied with a T joint with valve on both sides of the water heater. After an advice from handyman, I shut off the valve to the good water heater and turned on my main water supply. The torrential leak did not resume.

My question, what are forces in play here? was the valve to my broken water heater bad that it cause the torrential leak to continue or was it just that opening of main water supply increased the pressure causing the water in the tank to leak and closing of the second water heater reduced that pressure?

  • "a T joint with valve on both sides of the water heater." Yet you only speak of closing "the" valve. So is there a valve on the hot side and cold side of each water heater, or is there only a valve on both sides of the tee supplying the cold water to both?
    – Ecnerwal
    Commented Apr 11 at 1:42

2 Answers 2


Probably (your description is less clear than a good photo might be) you shut off the water to the "bad heater" but not the hot out from the bad heater, so it was connected to the water going into the "good heater" and back through the hot water line to the bad one.

There are multiple ways that two water heaters might be plumbed together, and we'd need a clear and unambiguous description (or clear pictures) to be sure what's going on with your particular set-up.

I note that you only mention closing ONE valve ("the valve") to the heater, so that's probably it. You would have to have, and close, valves on BOTH the hot out and cold in to properly isolate a heater. The hot out has no magical way to know that you don't think of it as being another direction for water to flow in.


Water can flow into a water heater from both ends so to disconnect a heater from the supply you need to stop water from both ends.

If a heater springs a leak water may also flow in from the outlet side of there is water pressure there.

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