In Hot Water

The retired water heater element

Introduction

So I did something new today; I replaced an element in my water heater. Despite dealing with pressurized water, pressurized air, and lethal voltages, I was not harmed by this experience. YMMV.

If you have an electric water heater, you might find this useful. If you have a gas water heater, you may find it interesting. If the thought of electricity or water leaks bothers you, don't be afraid to call a professional.

Why?

For the last few years, I've lived alone in my house. Recently, however, that has begun to change.

With more people comes more water usage, and after some complaints, I ran some numbers and concluded that the hot water didn't last as long as it should. I figured that I had an element that was either disabled, or malfunctioning.

Troubleshooting

I have an electric water heater with two elements. The upper element is close to the top of the tank and heats the top quarter or so of the water. The other element is very near the bottom and heats the rest. The reason for this is to speed recovery time; the bottom element will heat the entire tank evenly, but will take a long time, probably on the order of several hours, to do so. The upper element will heat the top quarter of the water volume to the desired temperature in a much shorter time. This facilitates waiting a short amount of time for a small amount of hot water, rather than waiting forever for any at all. Gas water heaters are able to transfer far more energy to the water than an electric unit, so they can get away with a single burner at the bottom of the tank.

Since I was living by myself and I take quick showers, I didn't notice that my hot water capacity was reduced, or if I did, it didn't cause me enough concern to investigate. However, once I gave it some thought, I decided to start my search with the lower element, since its failure would produce exactly the symptoms I was seeing: a small amount of hot water with only a short wait for more after the water ran cold.

I started by exploring the possibility that I had turned off the lower element in the past and simply forgotten about it. As I said, I use very little hot water compared to the average family, so keeping 150L hot at all times would have been a waste. Each element has its own thermostat, since they operate independently, so I removed the lower access cover on the tank to check the appropriate one. As it turns out, I have two different thermostats. The upper one was calibrated in degrees, so you could set your tank to the appropriate temperature. The lower one, however, simply had demarcations of "hot", "A", "B", "C", and "hottest". The dial was set to "A", so I turned it to "B" to see if that would have any effect.

It didn't. Since the water would transition from hot to cold, rather than hot to warm, and the lower thermostat wasn't turned down all the way to start with, I figured the cause might be more serious than a simple maladjustment. So on the theory that the lower element had failed, I tried a simple resistance check. Now, a heating element is basically a large wire, so a working one should have a low resistance, while a resistance of zero or some very high number would indicate a malfunction. After turning off the power to the heater and opening the upper and lower access covers, I disconnected the upper element to isolate it for measuring. An ohmmeter connected across the terminals indicated 0.019 ohms of resistance, which gave me a reference from a known-working element.

I then turned my attention to the bottom element. However, after disconnecting it, the ohmmeter recorded an open circuit across the terminals. This reinforced my theory that the lower element had failed altogether.

So now I'm looking at replacing a heating element in an electric water heater, something I've never done before.

Parts Acquisition

I started with a trip to the nearest big-box hardware store. They had several heating elements on the shelf, with various different power and voltage ratings, and a couple different fitting styles. The data plate on my water heater indicated that it used 3000W elements, and operated on 240V. Armed also with a photograph of the part of the element visible from the outside of the tank, I was able to select the appropriate replacement. While I was at it I noticed that the store also sold various water heater thermostats. Since the thermostat on my faulty element was not actually calibrated for temperature, I decided to replace it as well, since then the two elements could work in concert to keep all the water in the tank at the same temperature, and I'd actually know what that temperature was.

Air in, water out

Purging the tank

Unlike a gas water heater, in which the burner is kept separate from the water, the elements in an electric heater are immersed in the water they are heating. This improves the efficiency of heat transfer from the heating element to the water, but it also means that replacing an element requires draining the entire tank. This isn't as easy as you might think, especially when you're dealing with a ten-year-old tank. The drain is near the floor, and since I don't have a floor drain in the basement, I needed to drain it through a garden hose. However, the nearest drain was the laundry sink, which is above the level of the drain in the tank. Somehow I needed to make water flow uphill.

Now this is a purge kit

Enter the plumbing supply store. For about $6.50, I got a couple fittings that let me connect my air compressor to the faucet on the laundry sink. This allowed me to push air through the hot water lines, into the top of the tank, and force the water out of the drain. At 10psi it took about 20min to push all the water out of the tank.

Now, if you have a little compressor designed for, say, a brad nailer, then this isn't the best option for you. You may very well end up burning out your compressor, since you're going to try and pressurize a 150L tank to 10psi. Of course, if you have something a little bigger, say one designed to fill a 75L tank, you're good to go.

Removing the element

Once the tank was drained, I was ready to remove the heating element. Four bolts secured this particular element to a flange on the side of the tank, and once those were removed, a little twist with a screwdriver was all it took to break the element loose. I didn't know what to expect as I pulled the element out of the tank, but the corroded condition of it didn't surprise me in the slightest. What did surprise me, however, was the sediment at the bottom of the tank. I mean, I knew to expect some sediment, but I had no idea what it would look like, and I certainly didn't expect to see what I saw.

The sediment in the tank

Clearing the sediment

After getting over the sight of ten kilos of granola in the bottom of my hot water tank, I set to work cleaning it out so I could see what the inside of the tank looked like. Turns out the opening for the element is large enough to admit the wand of my shop vacuum, but just barely. I could put the wand straight in, but the tank has a concave bottom, and twisting it around to get to all the nooks and crannies in the bottom of the tank was impossible.

What I vacuumed out of the tank

After a little searching for a solution I came up with a piece of scrap hose from my rain barrel, which I taped to the end of one of the wands. This had a little curve at the end which made it possible to remove nearly all the silty crap from the bottom of the tank. Afterward I was able to see that the inside of the tank was in pretty good shape, surprisingly so for a tank of this age. Since I'm in the middle of replacing my kitchen, I was glad I wouldn't have to fork out another few hundred dollars for a new water heater right now.

Installing the new element

Installing the new element turned out to be simple. Once the access hole was clear of crud, I placed the seals. There's one that goes in the hole and one that seals the element's flange against the tank flange. The thermostat just sits against the tank wall to measure the temperature, and it's held there by a bracket that bolts on with the element. Once all that was in place, I connected the wires, using the photo I'd taken earlier as a guide. The instructions warned against over tightening the bolts, so I tightened them up as much as I dared without reefing on them.

Testing

I wanted to test for leaks without having to fill up the tank with water, since it would mean draining the entire tank to fix a leak. I would rather fill the tank with air and use a soap spray to check for leaks, as it's less messy. Fortunately, I had just the tool for the job. The little collection of fittings I'd made for purging the tank would also serve this purpose. After closing the drain on the tank and all the other hot water valves in the house, I pressurized the hot water lines to 10psi and sprayed the element with a little soapy water. The appearance of some foam prompted me to take a few more turns with the ratchet. After being satisfied that the element was properly sealed, I decided to remove a little more sediment before I filled the tank completely.

Margaritas anyone?

Flushing

By opening the drain line before turning on the water supply, I was able to splash some water into the tank and flush a little more of the sediment out. Thankfully, water heaters draw their hot water out of the top, so the crap that sits in the tank doesn't end up coming out of the faucet. However, it also means that your water heater will slowly fill with crud and eventually fail, as mine did, so it's a good idea to flush the tank once a year. This can be as simple as filling a bucket from the tank drain, which will flush out some of the sediment. Various sources have told me to turn off the water supply and drain the tank halfway or more before turning the water back on, effectively stirring up the sediment to allow it to flush better. All I know was I was able to get some really nasty looking water by letting the first few litres of water go straight out the drain. Once the drain was running clear I closed it and allowed the tank to fill by leaving a hot water faucet open until the air rushing out was replaced with water. After letting the tank sit under pressure for an hour and finding no unwelcome moisture, I closed the circuit breaker and let it heat up.

Conclusion

So, I now have far more hot water that I did before. The tank hasn't exploded or leaked all over the floor, I don't see any sparks or smell any smoke, and I have enough water to draw a proper bath. Oh, and I also have ten-odd kilos of icky granola-looking crud that leaves me thinking, "If that's what settles in the tank, what about the stuff that doesn't settle?"

Cheers.