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I have a leaky pipe on the hot water side that I'd like to fix. Following the pipes back to the water heater, I don't think there's a shutoff valve installed anywhere in the line, not even at the water heater outlet. At least, not one that is obvious for me to identify. How inconvenient!

I definitely have a shutoff valve on the cold supply inlet. What is the correct way to "turn off" the hot water so I'm not swimming when I disconnect the leaky pipe? The water heater is in the basement and the pipes in question are a few feet higher than the water heater.

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    While you're busy fixing the leak, you may want to install a couple of valves on the hot side. Maybe one on the outlet side of the heater, and since the hot water side is now empty, put a valve under each faucet (or other outlet, like the dishwasher). You may even want to "go crazy" and put valves on the cold side of each fixture, as well. It'll save you a ton of effort later. – FreeMan May 26 at 13:20
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My approach would be to turn off the water heater and the cold supply.

Then open a hot tap below, or as close to the area of the leak, to drain the hot pipe.

Then be prepared to catch the remaining water when you cut the pipe around the leak.

Supplement: One can get “ice clamps” that can be used to isolate either side of the leak but can be fun if the water pressure pushes the ice plug out...

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    Make sure the water heater contains only COLD water before disconnecting any pipes on the hot side! (The cold side isn't absolutely safe either.) – fraxinus May 26 at 10:54
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    +1 to fraxinus' comment - seems like a step needs to be added, namely run the water with cold supply open but water heater off, for at least a reasonable amount of time to make the hot water no longer overly hot... – Joe May 26 at 20:42
  • @Joe depends where the leak is exactly, but the op said it was above the water heater, so then the only water above the leak should be that contained in the pipes above as the water heater won't be supplying water as its supply is shut. – Solar Mike May 26 at 21:00
  • @SolarMike But won't the pipe between wherever you're draining it from and the water heater still have hot water in them (unless it's been a long time since you've run any hot water, anyway)? Especially if this is relatively close to the heater? – Joe May 26 at 21:03
  • @Joe what was the last line in my answer? – Solar Mike May 26 at 21:04
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Another simple and easy approach might be a repair clamp, search term " repair clamps for pipe leaks". Must meet the correct requirements like temperature, pipe type, drinking water compatibility.

A drainage could be avoided, and thus the danger of destroying old valves by closing and opening them the first time after decades.

If it is an old standard valve that is already leaky, the stem (compression) sealing package could be the cause. A simple tightening of the pressure nut may help.

The thermal insulation (re-) applied afterwards should have the same thickness all over the pipe - that way this clamp location could be easily identified.

And the cause for the leak should be identified. With metal pipes, the rule is from less noble to more noble in flow direction. F.e. the sequence copper - steel - copper could produce corrosion pits. Copper can only be used if the water meets the requirements for copper (ion types and quantity, acidity).

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I had this with a previous house. I've also had a house where in spite of having a hot water shut-off, the valve was leaky and was mainly only useful for damage limitation. The solution is pretty simple - turn off the cold water inlet and drain down the entire system, hot and cold.

This will be time-consuming with the heater in the basement, of course. Drain the pipes at ground level first, as best you can. Start by opening all taps/faucets. After that, if there is a suitable drain valve and hose connector then use that to drain down the remainder of the contents of above-ground pipes. Finally you'll have to drain the pipes in the basement into buckets. If you have a suitable pump then you may be able to just drain into a bucket and have it pumped out for you. (Since this is likely to happen again in future, I suggest investing in a pump would be a very good idea.) If not, you'll just have to get several buckets and bucket-brigade the water out of the basement.

If you can guarantee to have the fix completed quickly, then a pipe freezing kit (such as this one for example) can shut off water in a pipe temporarily by creating a frozen "plug". These kits are great for professionals who can get the job done rapidly and have all the right tools and parts to hand. As a DIYer though, you can usually expect jobs to take longer than you expected. I would 100% recommend not using a pipe freezer for any repairs you'll be doing, because there is an extremely high risk of the pipe unfreezing while you're working and filling your basement with a couple of inches of water! Do it the safe way instead, and drain the system down. It's much better to regret a bit of time and some aching muscles than to regret Katrina-style flood damage.

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    While a leaky valve is certainly a major pain, why would someone have to drain the entire supply side of the system? There's no need to drain the cold water side of the system to repair the hot water side. One simply needs to get the water level below where the leak is so the leaky bit of pipe can be repaired. – FreeMan May 26 at 13:18
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    @FreeMan The OP says that the leaky bit of pipe is only a few feet above the heater, so that clearly puts the leak somewhere in the basement level, or at most somewhere in the space between the basement ceiling and ground floor floorboards. Yes, you could avoid draining the small amount of piping between this level and the basement floor. But you need to drain the entire system above that point, including any header tanks, and the cold side needs to be shut off and depressurised so that it doesn't refill the hot side. – Graham May 26 at 13:30
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    @FreeMan ... You also have the problem of how to work out where the water level is. "The leak doesn't seem to be leaking any more" is not a good method when the system is depressurised. If there's a sink in the basement then great - open the taps and wait for it to stop flowing. If there isn't though (and typically there isn't because it would be lower than the house's waste outflow!), then the only sure way is to drain it down completely. – Graham May 26 at 13:36
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    Assuming your basement has a sump pump (if it doesn't, you might want to seriously consider getting one!), you can also go drop ~$20 at a hardware store for a hot-water rated hose, connect it to the drain valve of your water heater, and drain it straight into the sump. Although ... (con't) – Matthew May 26 at 14:43
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    (con't) ...with the system not pressurized, I'm not even sure this is necessary. If the pipes are all above the heater, you should be fine, and even if not, as long as there is some air in the lines so you don't have a siphon, water shouldn't flow out of the heater. (You might need to drain just a bit to ensure you have an air gap to prevent siphoning, but you probably don't need to completely drain the heater. You do need to drain the outgoing pipes, but if you don't have header tanks or the like, that shouldn't be very much water.) – Matthew May 26 at 14:44

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