Q&A for How to Flush a Water Heater

Acid is used but it is a professional task and the acid used will depend on the construction of the heater.

That will not work. When you turn off the cold water valve at the top, then no hot water will flow. The best bet is to turn off the heater (gas or electric) and take a shower. The water will slowly get colder as the hot water is used up and replaced by cold.

There are many things it could possibly be. 90% of the time, one of the elements have to be replaced (normally the lower one). Then there is the thermostat, the dip tube, sediment, etc.

You have closed the cold water intake valve and not opened a hot water sink tap to allow the pressure to drain off and allow air into the top of the tank. Like holding the top of a straw filled with water.

Sediment may be blocking the drain. If it so plugged that no water comes out at all, you can use a portable air tank to blow air into the drain hose. Always make sure you have a hot water valve open somewhere.

Check the line from the water heater to the sink. There maybe something blocking the line, a piece of rust if the water heater has a bit of age on it.

Probably not. Your hot water pipes are probably obstructed, most likely from the plastic stand pipe inside the heater disintegrating and leaving particles in the pipes. You will either need to replace or repair the water heater and flush out the pipes.

No. The tank automatically refills with cold water as the hot is used, so there is no loss in water volume during this time.

You may want to check for sulphur in your water if you are on a well-based system.

How did sand get in? Anyway, you're going to have a hard time. Drain the tank, then open up the supply at the top and hope that the pressure washes out some of the sand.

Yes, if the drain is functioning properly and can handle the volume of water being flushed.

Sounds like well water with iron bacterium and/or hydrogen sulfide. You should have your cold water tested to see if treatment is needed. You will also need to flush out your hot water heater and sanitize your pipes by means of bleach or hydrogen peroxide (please reference the correct procedure online, or hire a professional if you are not comfortable doing it yourself).

After draining, open the valve at the top and hope that the inrush of water will flush some of the sediment out.

On the bottom of the water heater, there is a spigot that a garden hose can attach to. But the water will not drain from that spigot until the release valve on top of the water heater is opened.

No, it will not harm the heater, but you should dilute the bleach with water. Pure bleach is unnecessarily strong.

There is probably sediment in the bottom of the tank, like a bunch of sand or little particles, that you are stirring up when you run water through it. Try flushing it; that should fix it.

As the hot water is used up it is replaced with cold water and mixes in the tank, hence cooler water making you turn the shower valve to hot.

Normally there is a pipe on the side of the water heater. It's attached to the pressure relief valve at the top. If there is excess pressure, the hot water will flow through the pipe downward through the pipe on the side.

Draining a water heater completely would probably take around 30 minutes.

Yes, because you are draining the water from the heater tank and you don't want the flames to turn on while you have an empty tank, as that could seriously damage the unit.

It's inside the tank. It's a pipe that runs from the cold water intake all the way down near the bottom of the tank. Cold water enters the tank from the bottom, and pushes hot water up to the hot pipe you see at the top of the tank.

If you cannot confidently follow the directions above, then you should call a plumber. If you have tried to flush it but it did not work, then you also need to call a plumber.

It's a toggle valve located on the outside of the tank, near the top. You can identify it as its discharge is into a pipe which leads down and is open at the end to allow an over-pressurized tank to vent to the atmosphere (also to your floor). To open the valve, pull the toggle and open it 1/4 of what a full rotation would be. Be extremely careful with the water, as it will be very hot.

No, it’s generally sulfur coming from your well water. (Metropolitan water supplies treat all their water before it even gets to your tap, so this answer is assuming your water supply is coming from a private water well.)

Yes, as long as you’re positive the floor drain isn’t clogged or backed up with anything! Lots of floor drains get clogged because people think they can clean their floors and wash anything down floor drains, but floor drains get plugged up easier than any other drains from being on the floor! Just use extreme caution when draining anything down a floor drain, because once they clog up, they’re rather difficult to clear!