The hot water system isolation valve: find it before you need it
It is the small valve on the cold water line to your system. And on the day a pipe or tank leaks it is the first thing worth reaching for. Most owners cannot say where theirs is.
An isolation valve is a shut-off valve on the cold water pipe that feeds your hot water system. Close it and fresh water stops flowing into the system. If something is leaking, that can limit the damage until a licensed plumber arrives.
Find yours this week, while nothing is wrong. Trying to trace pipes with water running across the floor is a poor time to learn.
Where do you find the isolation valve?
On a storage system it is usually on the cold inlet pipe close to the tank, often with a handle or a lever. On many installations it sits near the tempering valve or the relief valve, though the exact layout varies by model and by installer. Continuous flow units mount on a wall and have their own inlet valve nearby.
Follow the cold pipe that enters the bottom or side of the tank. The valve is somewhere along that run. If you cannot find one, that is worth knowing too, because it tells you the only option in an emergency is the main shut-off for the whole house.
| Valve | What it stops | Who should operate it |
|---|---|---|
| System isolation valve | Cold water flowing into the hot water system | You can close it in an emergency. Servicing or replacing it is a plumber's job |
| Main water shut-off | All water to the property | You, in any emergency |
| Relief valve | It is a safety release, not a shut-off | Nobody but a licensed plumber |
When is it worth closing?
Close it if water is leaking from the tank, the connections or the pipes around the system. Or if you are waiting for a plumber and want to stop more water coming in. It also helps if you have to be away from home with a fault you cannot fix yet.
Closing it does not make the system safe to leave running. A tank that is still heating with no water coming in can build up pressure and temperature. Switch the power off at the switchboard first where the system is electric, then close the valve, and call a licensed plumber. Do not open the relief valve to "let the pressure out". Our guide to the relief valve explains why it stays untouched.
Does a stiff or seized valve matter?
Yes. A valve that has not moved in years can seize with mineral scale, and then it is no use on the one day you need it. Do not force a seized handle with a wrench. You risk snapping the stem and starting the very leak you wanted to stop.
If your valve will not turn easily, tell your plumber at the next service. Replacing a worn isolation valve is a quick job for them and far better done on a calm day.
What is yours to do
- Locate the valve and the main shut-off. Tell everyone in the household where they are.
- Check you can reach it. A valve behind stored boxes is a valve you will not close in time.
- Look for drips at the valve. A weep around the handle or the joints is worth reporting.
- Mention it at the next service. Ask the plumber to confirm it turns and seals, and note it if it does not.
The warranty terms on your system often call for a licensed installer, so keep any work on this valve with one.
Frequently asked questions
Where is the isolation valve on a hot water system?
It is normally on the cold water pipe that enters the system, close to the tank or the unit. It may have a handle or a lever. If you cannot find one, the main water shut-off for the property is the fallback in an emergency.
Can I close the isolation valve myself?
Yes, closing it in an emergency is something you can do. Replacing, adding or repairing the valve is licensed plumbing work. On an electric system, switch the power off at the switchboard as well.
Is closing the isolation valve enough to make the system safe?
No. It stops water coming in, but a heated tank can still build up pressure. Isolate the power at the switchboard, and call a licensed plumber. Never tamper with the relief valve.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- Australian Government, energy.gov.au. Hot water systems — types, installation and energy performance
- Australian Building Codes Board. National Construction Code — Volume Three (Plumbing Code of Australia)