When you want to return your hot water heater back to normal operations, re-attach the cold water inlet pipe. Remember to tighten the compression fittings at both ends of the pipe. You can use teflon thread tape over the olive (not over the threads in this case) to give a really good seal. I didn't use any and mine isn't leaking. Tighten the nuts reasonably tight but not as tight as you can possibly turn them. Brass is pretty soft compared to steel and you don't want to damage anything by overtightening.

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If you live with other people who are completely freaked out by the whole idea that eventually there will be no more town water, you can use the maintenance reason as an excuse: You could say you're draining it for maintenance, although the main reason may be to practice draining your hot water heater for survival water.

The garden hose now fits perfectly onto the water heater. The next step is to open a hot tap (e.g. at the laundry sink), allowing air to enter the top of the tank. This release the air lock and the water can drain out through the hose.

The float type LWFCO design shown previously is fitted with its own blowdown valve which is maintained according to the boiler manufacturer’s instructions and the applicable standards. The LWFCO device is tested by means of opening the blowdown valve and observing whether the burner is shut down when the water level in the water column falls below the defined low water level; another procedure used to prove the working of the LWFCO device is the evaporation test.

When that is done you can loosen the nut at the heater end of the cold water inlet pipe. I was wondering how much water would come out as I was doing this. It turned out that hardly any came out, just a few drips.

If you have an instantaneous type then — sorry — you don't have any more water in your water heater than in any other short length of pipe in your plumbing system. You may still be able to get some survival water out of your plumbing system.

Unless you're already a plumbing expert, draining your hot water heater is one of those things that's much easier to do once you have already done it. So it's a really good idea to practice draining it. Since it's part of regular maintenance (that a lot of people ignore) it's a good idea to do it anyway.

You can also see the cold water inlet connection to the hot water heater (before I did anything to it), and the grey electrical cable. I thought it was going to be annoying how the power cable runs right under the cold water inlet to the heater, but it didn't really get in the way at all.

IMPORTANT: This part of the process may or may not be legal to perform (assuming you're not a licensed plumber), depending on your country and state.

A typical Australian storage-type hot water heater. This is a 250 litre model, mine is a 315 litre. If you have a similar system at home then you have that many liters of emergency water available at all times. A person needs 2-3 litres of water a day as a reasonable mimimum intake. Learning to drain your hot water heater means you can survive for at least 100 days (divided by how many people you have) with no other water supply.

Alarms as well as shutdowns are usually connected to the LWFCO device. For example, an alarm will sound upon a low-water level scenario and for a high-water level scenario.

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IMPORTANT: Be aware that once you do the next step of disconnecting the cold water inlet pipe, there will be nothing (other than maybe some air lock effect, or you attaching a hose, or re-attaching the inlet pipe) to stop all the water in the water heater flowing out onto the floor. Expect to get at least your knees and toes wet. When I did this there was less water spilt than I expected, but this may not always be the case.

The phenomenon of drum swell and shrinkage primarily affects larger boilers, requiring the use of advanced water level measurement and fuel cut off devices. This article addresses fuel cut off devices for smaller units only.

In the next photo the pipe is completely off and there is still not that much water spilling. There's 315 litres of water in the tank above this outlet hole, and nothing stopping it from flowing out apart from the air lock inside the tank. On the left you can see what the end of the pipe looks like. The plastic sealing ring is called an "olive" and the whole connection is called a compression fitting.

The probe type LWFCO device uses conductivity probes to detect the water level, cutting off the fuel supply if the water level falls below the minimum requirement. Probe type LWFCO devices are generally robust and require minimal maintenance. Probe type LWFCO devices are housed within a sleeve or chamber to increase their reliability.

The pipe didn't come out easily so I tried hitting the pipe (not too hard) with a soft hammer to loosen it up. I'm not sure how much this helped since I did it before I discovered a better method.

Turn off the electrical power switch to the hot water heater. If you have a gas hot water heater, turn off the gas to it. If you let an electric hot water heater try to heat while the tank is empty it could destroy the heating element. Turning off the power will eliminate this problem.

This will be another web page coming soon. But, basically, turn off the mains supply, then turn on the tap on highest water outlet in your house (which may be your shower) to allow air into the pipes. Then get some buckets and turn on the tap on the lowest outlet (that's far away from the other one) and see how much water comes out. This is quite easy to do and doesn't need any tools or fooling around with the plumbing. The greater the difference in height between the two taps (e.g. if you have a sloping block of land, and/or a multi storey house) and the longer the pipe distance, the more water will be there. You could also try forcing the water out by connecting an air hose to the upper tap and forcing air into the pipe, using a foot air pump or something like that connected to the tap.

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A boiler drum contains the water reservoir that is circulated within a steam generator. Watertube boilers have a steam drum above the boiler tubes, whereas firetube boilers have tubes within the boiler drum. In both boiler designs, water heated by the tube walls is also cooling the tube walls; thus a low water level scenario will lead to overheating of the tubes and potential boiler failure.

If this was a real survival situation, and there was no mains water, you would have no choice but to wait a few days (approximately) or until the water inside the water heater was cold enough to touch. This means that if the mains water was to suddenly go off, you won't be able to use the water in your hot water heater for a few days (or maybe a day or two if the weather is really cold and your water heater is outside). Of course if you've had no electrical power (or gas if its a gas system) for several days or longer, the water will all be cold and you can skip this step entirely.

Good to know – this article is part of our Power Engineering Fundamentals online course. Check it out if you want to learn more about boilers, HRSGs, turbines, transformers, and power plants.

If you have a storage tank type, you have a supply of water that can be used for survival purposes if this should become necessary for any reason — such as when the town water supply is cut off for an extended period of time.

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There are two types of hot water heaters, storage and instantaneous. Instantaneous heaters heat the water instantly as it passes through the heater, while in storage heaters the hot water stored in a tank. It should be easy to tell which type you have by looking at your hot water heater. If you can see a tank then you have a storage type. If there is no tank you have an instantaneous hot water heater.

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It may be true that since cold water enters from the bottom, then if you have an off peak system and have used some hot water that day, then the water at the bottom of the heater will be cold. Which may allow you (if you're somewhat experienced with plumbing work) enough time to disconnect the pipe and attach a tap quickly before it gets too hot to touch. But I wouldn't mess around with this. If you don't flush the entire heater with cold water first, you'll have no idea of knowing how hot the water at the bottom of the heater will be until you disonnect the pipe — and then it may be too late/hot to reconnect it.

The next problem I had is that the hose adapter that I purchased did not fit. It was much too big and did not screw onto the thread. I had to take this off, push the pipe back in, and re-tighten the nut (hand tight was fine).

IMPORTANT: Before I attempted to do this, I had a look online for sources of information on how to drain a hot water heater. I found that there were a lot of other sources, BUT, all of the ones I found explained how to drain the water from the "drain valve" located at the bottom of the heater tank. Click here to see what some hot water heater drain valves look like. However, when I went to look for the drain valve, I looked, and looked, and..... There was no drain valve! If I had read in a book that I could use the water in my hot water heater for survival water, and I had no other water, I would be pretty stressed at this point.

I did some research and learned that my water heater, along with many Australian hot water heaters — perhaps most of them — does not have a separate drain outlet. This research included finding the manual and technical schematic drawings of my hot water heater, and talking to a plumber on the phone.

Then open the cold water inlet tap at the wall to allow the heater to fill. Note that you want to leave a hot tap open somewhere (e.g. a laundry sink), so that air can flow out of the top of the tank as water fills it up from the bottom. Once you see (cold) water flowing out of the tap and into the sink, that means the heater is full. Then, close the sink tap (like you normally would). Your hot water heater is now full of fresh cold water from the mains.

I was wondering how much water would come out as I was doing this. It turned out that hardly any came out, just a few drips.

For both LWFCO device types (float and probe), it is essential that blowdown testing be conducted at regular intervals to ensure that the devices are operating correctly. This is especially important with reference to probe type devices, which are more prone to fouling by sediment and scale in the boiler water.

Water heateroverflow pipe requirements

You can have a really long hot shower before doing the next step (and the rest of your family, if your hot water heater is big enough). Since you're going to drain all the hot water anyway, you might as well use it for something.

To maximise efficiency in watertube boilers, combustion takes place within a chamber whose walls are made up of water carrying tubes and/or tubes located directly within the flame or hot flue gases. It is vital that the tubes remain filled with water when the boiler is in operation; accurate and reliable water level measurement equipment is installed for this reason.

You will need a few tools to drain your hot water heater. The most important is a spanner to undo the nuts (either on the drain valve, if you have one, or on the cold water inlet pipes). You can use a fixed size spanner of the correct size, or a shifter spanner or wrench. If desperate you could use pliers or some other less ideal tool. Some heaters with built-in drain valves may not need a spanner.

I even went through a stage of reading about other people with the same problem, only to find that the drain valve was located behind a plastic cover. All they had to do was remove the cover and the drain valve was behind it. I thought that must be the answer, until I looked at my hot water heater some more, and looked some more, and, ... no cover either. Note that almost all of these web pages (and YouTube videos) aren't from Australia.

Even with the nut completely off, not much water came out. The next step is to pull the pipe out from the heater. This was quite hard since it was wedged in very tight.

I found that holding the pipe firmly while pulling in a series of hard short yanks (about 1-2 per second) was the best method. The pipe came out gradually and there was less water on the floor than I expected.

If there are still air locks in the piping for any reason (even with a hot tap open), you could also open the pressure relief safety valve to allow air to enter the heater and release the air lock. However you will have to stand there holding it open several times, so it's probably easier to open a hot tap if this works. Or try both if not much water is draining out.

Once the tap is turned off, loosen the nut at the other end of the pipe to the heater. This will allow the pipe to swing out away from the heater when you detach the pipe from the heater end. You can loosen the nut all the way until it comes off its thread.

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Before you begin, have a look around your hot water heater to become familiar with its connections. There are not many. Cold water enters from a pipe at the bottom, with a tap between the wall and the hot water heater. Hot water leaves from a pipe at the top, which may be covered with some insulation (since it's hot). There will be a connection for either electricity or gas, and a thermostat control for setting the temperature of the hot water. There will also be a pressure relief safety valve at the top of the heater, and probably a pipe coming down from that, maybe draining onto the floor. Maybe there will also be a drain valve at the bottom of the heater.

Then turn back on the electrical power (or light the gas). The state of your water heater now is exactly the same as in normal use if you had a really long shower and used up all the hot water. Now all you have to do is wait for it to heat up again. If you have an off-peak hot water system, this will happen overnight so you won't have any hot water until the next day.

If you're blessed with a hot water heater that has a separate drain valve, you wouldn't need to disconnect any plumbing, and you would attach the drain hose to the drain valve, and then open the valve.

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Here you can see the pipe halfway out, and there is some water spilling onto the floor. There is still less spillage than I was expecting. I think this is because there was a good seal inside the tank from having the pressure released and then the hot taps turned off.

Next, I'll update the page with more photos of flushing the sediment from the bottom of the tank, and how to check the pressure safety valve.

Water heater drainhose size

Float type LWFCO devices are connected to an electrical circuit which controls the operation of the burner and fuel supply. As LWFCO floats move proportionally with the boiler drum water level, any low water level scenario will cause the float to drop and the burner(s) to shut down.

If you let an electric hot water heater try to heat while the tank is empty it could destroy the heating element. Turning off the power will eliminate this problem.

Here is the 15 to 20mm thread adapter next to the 3/4" garden hose adapter that I originally purchased, and the end of a garden hose.

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The next step is to turn off the cold water inlet tap. This was difficult because the tap was so tight and at first I had to use a towel for extra grip. After a while it loosened up. You can also see the cold water inlet connection to the hot water heater (before I did anything to it), and the grey electrical cable. I thought it was going to be annoying how the power cable runs right under the cold water inlet to the heater, but it didn't really get in the way at all.

The LWFCO device has connections to the steam and water side of the boiler. The steam line from the LWFCO device connects to the top of the boiler drum. The water line from the LWFCO device connects to the drum at a level much below that of the boiler’s normal operating water level (NOWL).

The boiler gauge glass is installed at the same level as that of the fuel cut off device, and so any reduction in the water level detected by the fuel cut off device will cause a water level reduction to be shown by the gauge. At the time when fuel is interrupted, the water level should still be seen at the bottom of the boiler gauge glass.

When I got to the hardware store, all the threads they had were labelled 20mm and 15mm. I had brought the 3/4" hose adapter with me, and it fit perfectly on the 20mm threads. I thought this was interesting since in most other types of mechanics, imperial and metric threads are not compatible with each other. Usually the diameters are very slightly different, and, even if they do match closely enough, the number of threads per centimetre (or inch) is different. However with plumbing, I wondered if this must not be an issue since they seemed to be a perfect fit. After a search online I found a page which says that in Australia "It's all imperial here! It is just called by the nearest metric size... 15mm = 1/2inch, 20mm = 3/4 inch, 25mm = 1 inch".

Draining your hot water heater can also be done as part of regular maintenance of your hot water heater. Draining the heater to remove sediment is meant to be done periodically. This new web page also (eventually) will show how to check your pressure safety valve. Checking the valve is also a part of regular maintenance, and a stuck valve can cause your hot water heater to explode so this is a good one to pay attention to.

This page shows how to drain your hot water heater to obtain water, which could be used for survival purposes if your usual mains water supply was lost for any reason. If you have a storage-type hot water heater, there will be up to a few hundred litres of drinkable water stored in it at all times (unless you've drained it). If you don't have any other water source (such as rainwater collection tanks or your own dam), this will probably be by far your biggest source of drinkable water if there is no more mains water available.

You will also want a hose to drain the water from. I used an ordinary garden hose. If there is no drain valve, you will also want one or more adapters so you can connect the hose to the tank (these are pictured further down the page). It would also be very useful to have a small (or even full size) tap that you can screw on, so you can control the flow of water. Also some teflon thread tape to seal any threads that you unscrew may be useful. I found that it wasn't needed on the compression fittings that I have, which have plastic "olives" (pictured below).

It is important to install fuel cut off devices that interrupt a boiler’s fuel supply in order to stop the heating process if an emergency scenario should occur. A LWFCO device interrupts the fuel supply if the water level in the steam drum is too low, but the fuel supply may also be interrupted if the drum steam pressure is too high, drum steam temperature is too high, upon loss of flame, or for other reasons specified by the manufacturer or governing body (ASME, BS etc.).

A person needs 2-3 litres of water a day as a reasonable mimimum intake. Learning to drain your hot water heater means you can survive for at least 100 days (divided by how many people you have) with no other water supply.

LWFCO devices can also be designed so that when they shut down the burner, they also automatically start the feedwater pump, monitor the water level until it reaches the normal operating water level (NOWL) again, then start the burners once a safe working level is again reached.

Hose todrain water heaterHome depot

Once the cold water inlet tap is turned off, there will be no mains pressure supplied to the heater. Turn on a hot tap (anywhere in the house) and see that no water comes out. This will also release some of the pressure inside the tank. Then turn the hot tap off again to create an air seal / air lock that will greatly slow the flow of water out of the heater (and onto the floor) once you disconnect the inlet pipe from the heater. It's not critical if you skip this step, but if you skip it you'll probably get more water leaking onto the floor when doing the next step.

Content is copyright © Survival.ark.au 2005-2024 All Rights Reserved. Terms of Use. Definitely read the disclaimer before trying anything from this website, especially including the practices and skills. This website uses affiliate links – this doesn't cost you any more, but I get a commission on purchases made through the website. As an Amazon Associate I earn similarly from qualifying purchases.

The water took a long time to drain out, between 30 minutes and an hour to drain completely. Note that most of the hose in this picture isn't being used to drain the heater. It's better to use a short length of hose, since the water isn't under mains pressure, only the low pressure from gravity. A long hose needs more force for the water to flow and it might not drain out all the water. You also need the end of the hose to be lower than the bottom of the heater tank.

Since the aim of this is to drain the hot water heater, the next thing you need to do is locate where you're going to drain the water from.

Water heater drain tubereplacement

You only need to do this next step when practicing draining the heater (i.e. when there is still mains water available) and there has been power/gas available recently, but in that case it's very important. If you don't have any mains water and there has been power/gas connected to your water heater recently, the water in your heater may still be very hot. So read the instructions for this step anyway. In that case, you might have to wait a few days for it to cool down before doing anything else.

As explained above, after turning off the electrical power (or gas), let the hot water run out by turning on a hot tap until it runs cold. While the hot water is running, the heater will be filling up with cold water from the mains. I had a hot shower before this, and it still took another 15 minutes to run cold.

It is important to note that fuel cut off devices are not only installed for the purpose of isolating the fuel supply in the event of a critically low water level, but also in case of other events that may otherwise render the boiler unsafe or risk major plant damage (high steam pressure, high steam temperature, loss of flame, abnormal furnace pressure etc.).

At this stage, your hot water heater should be full of cold water, and the heating source (either electricity or gas) turned off.

If you are blessed with a hot water heater that has a separate drain valve, you don't need to do this step and the whole process is much easier.

In most boilers, the water that is heated by the boiler tubes to create steam is also the water that cools the tubes. Loss of this water can thus cause the tubes to overheat or even melt, leading to expensive and lengthy plant outages.

IMPORTANT: Some of the plumbing work needed to drain a hot water heater (especially if there is no separate drain valve) may or may not be legal to perform (assuming you're not a licensed plumber), depending on your country and state. The maximum penalty I've heard of for performing renegade plumbing work is the death penalty by torture and execution, which was scheduled for Robert De Niro's charater Archibald "Harry" Tuttle in the fictional 1985 movie "Brazil". (Warning: this movie is rated R and has some violence).

Water heater drainvalve

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What this means is if you don't have a separate drain valve, you have to drain the water from the cold water inlet by disconnecting the pipe from your plumbing. This web page shows you how to do this, and it's the only page I've found so far on the internet that does.

IMPORTANT: When turning a nut that's inline with other nuts like in the picture above (in this case there are two other nuts on each side of the tap), the one that's on the least tightly will unscrew. So be careful to check that the right nut is turning. If you turn the whole tap around enough times it will come off from the wall and cold water at mains pressure will shoot out until you turn off the mains supply (e.g. at the front of your house). If the whole tap was turning, instead of the nut you want, try holding the tap tightly with your hand to not let it turn while you loosen the nut.

IMPORTANT: Please read the legal section and disclaimer before attempting any of the skills or practices shown in this website.

Water heater drain tuberemoval

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The next step is to open a hot tap (e.g. at the laundry sink), allowing air to enter the top of the tank. This release the air lock and the water can drain out through the hose.

Water heater drain tubeinstallation

While the hot water is running, the heater will be filling up with cold water from the mains. I had a hot shower before this, and it still took another 15 minutes to run cold.

For industrial boilers, accurate measurement of the boiler steam drum water level is vital for a boiler’s safe operation. It is also important that the fuel supply to the boiler can be interrupted automatically in case, should the event occur, the operator fails to realise that the water level has fallen below a defined critical level. Low water fuel cut off (LWFCO) devices are used to measure the water level in a boiler drum and to interrupt the fuel supply should the water level be too low.

For firetube boilers, the water within the drum surrounds the tubes and it is the water level within this drum that is measured and connected to a low water fuel cut off device. It is also possible to install LWFCO devices on water heaters although these operate at much lower pressures and temperatures.

This is another reason why it's much better to practice draining your hot water heater when you still have plenty of water, rather than have a problem like this happen in the middle of a "survival situation".

Water heater drain tubesize

Before I started the whole process of draining the hot water heater, I looked up the size of the inlet thread in the water heater manual (which I found online), and it said 3/4" (that's 3/4 of an inch). So I bought a 3/4" brass hose adapter (as shown above) and expected this would screw right on. However I wasn't looking closely enough, and the 3/4" refers to the female thread in the heater itself. The male thread you can see here, on the other end of the male-male adapter that's screwed into the heater, is a smaller size.

I had to go back to the hardware store and get one of these, an adapter with a 15mm female thread and a 20mm male thread on it. If you were doing this in a real survival situation it would also be really good to have a small tap to put on here, so you can turn the water on and off. Or use a trigger nozzle at the other end of the hose.

The below image shows a typical low water fuel cut off device; the device shown is of the float design. A boiler gauge glass may be integrated into the LWFCO along with try cocks (small red valves used to prove the water level in the water column). The LWFCO device may be incorporated into a boiler water column depending upon the boiler design.

DANGER: The step is especially important if your hot water heater does not have a separate drain valve. Remember that when there's no separate drain valve you'll be draining the heater by disconnecting the cold water inlet pipe from the plumbing. If your water heater is full of hot water, once you disconnect the inlet pipe, hot water will gush out of the hole. Without highly specialised gloves you won't even be able to touch it again to connect a drain hose, or do anything other than run outside and try not to get burned by the few hundred litres of hot water that's now draining onto your floor (and possibly spraying around too).

THIS STEP IS VERY IMPORTANT: Assuming there has been some electrical power and/or gas connected to your heater within the last few days, the water in your hot water heater is veryHOT! It's a really good idea not to drain the heater when its full of hot water. The water inside the heater can remain hot for several days after the power has been shut off.

You could also use other combinations of adapters here, e.g. a if you could find a 15 to 25mm thread adapter you could connect this to a standard 1 inch hose adapter (like is found on most garden taps) instead of needing the unusual sized 3/4" one.

It took me a whole day to perform this entire procedure, including making an unexpected trip to the hadware store, and taking all the photos and making notes on what I was doing.