I need to change the hot and cold flexible water pipes feeding my bathroom sink as they are rusty and ready to burst. The problem is there are no shutoff valves under my sink so I'm wondering what the best course of action is.

I've read all the blogs I could find and found the information to be confusing as everyone had a different piece of advice.

  • Some people say that shutting the main valve at the meter and draining the hot/cold water pipes is sufficient as long as the water heater is lower than the lowest hot tap that will be drained (hard to say for me as my water heater is on the ground floor)
  • Some people say that the water heater cold water feeding pipe valve should be shut off
  • Some people say the water heater should be turned off (gas, electricity) as a precaution
  • Some people say the water heater might get siphoned out and therefore present a hazard, etc.

Can someone help me knowing that my bathroom is on the first floor and my water heater is on the ground floor? I realize I need a better understanding of the theory so if someone knows where to find some good information please let me know.

  • Thank you very much to all of you for taking the time to reply. The funny part is that my neighboord now would like me to change his flexible water hoses too but his house is different as he has a solar panel with a big tank on his roof to generate hot water, can you tell me what I would have to do differently in order to change his hot/cold flexible hoses? Thanks a zillion!!!
    – Wayne
    Commented Apr 29, 2017 at 0:20

3 Answers 3


The water heater should have an vacuum relief valve, so no siphoning should happen. The water heater is designed to withstand a loss of pressure on the cold side without any problem, no matter if the hot tap is open or not.

Consider this: if you close the main shut-off, this has exactly the same effect if the water was turned upstream from you, on the street, or if the water main burst somewhere, etc. So this poses no hazard to you or your water heater, as these things happen from time to time, and your water heater is designed to handle them.

Just close your main water shut-off, open the taps you are changing water pipes for, both cold and hot, and let the water drain. Hopefully your main water shut-off is operational, and withing a couple of minutes, water stops flowing, then you may proceed. But wait till the water is completely stopped: any trickle may indicate that your main shut-off does not close properly.

  • 1
    I agree there will still be water in the tank and if the water is only shut off long enough to replace the lines it should be fine, more than a couple of hours I would shut of the water heater. While you have the lines disconnected it would be a good idea to install shut off valves.
    – Ed Beal
    Commented Apr 28, 2017 at 13:25
  • It's not the same though. If the city turns off your water that doesn't also disconnect any of the pipes inside your house. Commented Apr 28, 2017 at 13:45
  • @Harper: A disconnected pipe and an open tap is exactly the same. Guess what happens when city turns off your water while you're taking a shower?
    – haimg
    Commented Apr 28, 2017 at 13:47
  • There are only two concerns about turning off the water heater: (1) running it without water is bad and could damage it. (2) while the water is shutoff, heating the water is pointless since you can't use it. If there's no chance of the tank draining, and the water is not going to be off for very long (eg, a couple hours), neither of these is an issue.
    – gregmac
    Commented Apr 28, 2017 at 15:13
  • Also the other thing I'd add is if you are dealing with copper pipes, make sure there's absolutely no water within a foot or so of the pipes where you're soldering, or you'll never get a clean connection. Even a dribble of water coming into your joint is enough to screw it up (the old trick there is to put some bread in the pipe to stop the water, which will get flushed out later). With PEX or push-on connectors this isn't a concern.
    – gregmac
    Commented Apr 28, 2017 at 15:16

My first advice is always err on the side of safety. Others may have other solutions, but I would not want to take chances of having a watery mess in the house, or burning up a water heater element if it becomes drained.

If your hot water heater has both the inlet and outlets on the top of it, you will not have to turn the power (gas/electric) off, but it will not hurt to turn it off. You will need to still shut off the water supply to the whole house. Since you say there are not shut off valves at the sink, you will need to stop water flow at the easiest place - the house inlet.

You will NOT have to drain the hot water heater if both the inlet and outlet are on the top, or if the outlet is on the top and the inlet is the side or bottom. Why? Because the water in the tank will not be pressurized once the house water inlet is shut off. The hot water will sit in the tank like a cup of coffee sitting on a table. As long as you don't try to refill the cup, the liquid in it will not go anywhere. That's your main example - non-pressurized water won't flow uphill, only downhill.

You will have some water drain from the pipe at the sink once you take it off. Gravity will drain most of the water from the line to the lowest open point, i.e. at your sink. If your house is 2 story, there may be water in the lines from above that will drain out. So have a good size bucket handy. There will be no way to avoid some water draining, so have rags too.

If your water heater has outlets on the side, you may have no choice but to allow it to partially drain. It will drain out whatever capacity it has until the level goes below the outlet on the tank or the highest water pipe in the walls.

After the job is done, the water heater will refill when you turn the house water back on, and then turn the power back on to reheat the water.


Don't just turn off the water heater. Turn it off 6-8 hours before the work, so you don't have to worry about scalding hot water bursting out unexpected. You can't fix a serious burn with a mop! Hard to finish the repair too.

Also be prepared for the possibility that the shutoff valves won't shut off entirely and may dribble. Which can be super annoying when you're trying to solder. Opening a faucet/spigot upstream or lower should help.

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