Do I need to turn off my hot water heater if I shut the water main to my house? (IMPORTANT)

In most homes, the hot water heater is located directly adjacent to the main water supply. If you’re shutting off the water main to your home or property, you may wonder whether you need to turn off your hot water heater as well. You do not need to shut off your hot water heater specifically; it will automatically go offline when your home loses access to fresh water. There are some exceptions though!


 If you plan to close the water supply for a longer period of time, it can be a great idea to turn off the water heater as the tank can run out of water and this can cause some problems. This is not really a problem with tankless systems. In both cases, it is a great idea to open all the faucets after you have closed the water supply to remove as much water from the drains and heater as possible.

Leaving the water heater on has its advantages though if you have a tank. Standing water in your pipes can lead to dangerous situations. Bacteria can grow in the tank and pipes. Water heaters with a tank often have a dedicated program that heats up the water to remove these. If you turn the system off, it is not able to do this anymore. If you drain the water from the pipes and tank by opening the faucet after you have closed the water supply, it shouldn’t be too much of a problem. A water tank can contain a lot of water though so you are going to have to flush a lot of water when you do this. It won’t be possible to remove all the water from the pipes so there can still be some damage.

Unfortunately for those trying to avoid freezing their pipes in the winter, there are several hidden dangers in leaving these systems online without fresh-water pressure at a constant stream.

What happens when you don’t shut off the water heater?

When the water main to your home is shut off, the water pressure inside your pipes will drop. When this happens, your water heater will lose its constant supply of water and heat. Most systems have sensors that will shut it down when they notice that there is no water pressure. 

The water heater will probably show an error code on the display to indicate that it doesn’t receive any water. It might beep and make other noises.

When you reopen the main water supply, you might have to press a button on your water heater to restart it. Some systems do this on their own. Check the water pressure in your system by looking at the pressure gauge. If the pressure gets too high, water might flow out of the expansion valve.

Older systems might not have these sensors and the manual of your device can indicate that you have to turn it off anyway. You can look this up by Googling the moel number of your water heater to see what the instructions are for your heater. 

What happens when you turn off your hot water heater?

The system will shut down. If you have a tankless heater, nothing should happen. Some water might drip out of it or the faucet. If you have a heater with a tank, the water inside the tank will cool down. As discussed before, this can lead to dangerous situations if you leave it like this for a long period of time.

The water inside your pipes will start to cool down as well. During the winter, this can lead to frozen pipes and cause a lot of damage. This is something that you should avoid at all costs as it can require expensive repairs!

Water heaters are quite advanced and the processor inside the system can turn down the motor and other parts so that they don’t get damaged when you shut them down.

How to properly shut off the hot water supply to your home

Make sure that no one in your house is using hot water before you shut it off. The best approach depends on your system. Most systems have an off button. It can take some time before the water heater shuts down. Older systems don’t have this and you just have to unplug them.

This is also a great moment to inspect your system. Do you see any error codes on the display? Do you see water around the heater? Are the filters cleaned? A lot of people don’t spend enough time maintaining their water heater and this reduces the efficiency of the system. You can adjust the temperature of your water as well.

Water heaters should be maintained often to keep them working properly. This should be done by a licensed plumber. They have advanced tools to check that everything works properly.

Conclusion: will shutting off water hurt the water heater?

When the water main to your home is shut off, the water pressure in your pipes will drop to zero. In many cases, this will cause your hot water tank to go into passive mode. You can turn off your water heater but this is often not really required. Always check the manual of your device to check what the manufacturer recommends though.

A water heater that is cut open.

 This is not a dangerous situation in itself, but it can lead to frozen pipes during cold winters if precautions are not taken. 

Don’t turn the water off for too long as this can lead to bacteria in the pipes and water. A special procedure is needed to get this cleaned out. You can open up your faucets to remove as much water as possible after you have closed the water supply but it is not possible to remove all the water.

Overall, most modern water heaters will shut down to avoid damage if they notice that the water pressure is too low. You will get a warning signal on the display. Some water heaters will start beeping as well.