I've noticed that my shower, which used to run hot water for what seemed like forever, now can only produce about 15 minutes of hot water. This doesn't appear to be related to other water usage in the house.
What are the possible causes of this? Could there be a leak in my water heater, etc?
If you have an electric hot water heater, it may mean that one of your two elements has burned out. Most electric hot water heaters have an uppper and a lower element; the upper runs until the top of the tank is hot, which provides quick recovery time, then when the top thermostat is satisfied, it transfers power to the lower thermostat, which heats until the entire tank is hot.
If you are getting less than a full tank of hot water, the most likely cause is the bottom element burning out. Less likely, either of the thermostats could be faulty, which could be keeping the lower element from turning on.
If the upper element were burned out, you most likely wouldn't get any water, since the lower element is usually not turned on until the upper one shuts off.
If you've got a gas water heater, there is a common problem that can occur with certain models. Because of the way they're designed, many have a "dip tube" that sits underneath the cold water inlet. It runs most of the length down the heater and channels incoming cold water down to the bottom of the tank where it can be heated closest to the flame.
If this breaks off part way (which I have had a few do, due to deterioriation of the plastic material), the net effect is that cold water is mixed near the top of the tank as the water is taken from the tank and it seems like it's running cooler or running out of hot water quickly.
You can pretty easily verify this by disconnecting the cold water inlet pipe from the top of the heater and carefully removing the dip tube to check its length.
For all the trouble, it's a couple-dollar part that can be ordered from the water heater manufacturer or a supply shop.
Shut the cold water supply off near the inlet, remove it, and pull the old dip tube flange out. Replace the tube with a new one, and secure the cold water inlet connection per code.
Hot water is again your reward.
The same defect happened to me a few years ago on my gas water heater. Hot water would last only a few minutes and then only cold water would be coming out.
The cause of my problem was that my dip tube, which send the incoming cold water from the top of the heater down to the bottom, was broken somewhere close to the top. After the tube sends new cold water all the way to the bottom near the flames (gas) or heating element (electric), once the water heats up, it goes up to the top of the heater, ready to be supplied out across the piping system:
If the tube is broken (typically at the top but could be anywhere along), which happens due to some chemical corrosion which I can't explain (perhaps minerals in the water, not sure), the incoming water does not reach the bottom of the heater, making the distance between the cold water and the heat larger, which reduces the amount of hot water your heater produces.
My gut feeling is that this is what your problem is. To check, you will need to dismount the (hopefully) flexible connector between the cold water supply pipe ends and the heater (I say hopefully because some people cut corners and run the pipe all the way to the heater, which is bad because it makes it harder to take things apart), and twist the socket off as the dip tube is mounted to it on the other side. When you pull it out, if the tube is much shorter than the heater, or the ending shows obvious signs of breakage, it means you need to replace the dip tube.
Hope this helps.
I can only assume that you have an electric water heater since I can't think of any way that this would happen in a gas water heater.
Anyways, as TomG has said, the bottom element is out. It's hard to say why it failed, but one possibility is that it became covered with sediment, overheated, and then failed.
The first step would be to drain your water heater to remove the sediment and to be able to replace the lower element.
This will forcefully drain the water heater, and hopefully the city's water pressure will be able to get a decent amount of the sediment out of the bottom. Depending on how fast the water is flowing, let this continue for 1-5 minutes. Sometimes the drain can be pretty clogged up or the bottom quite full, and the water won't come out very fast, especially when you disconnect the city's water pressure.
This will drain the water heater. The open hot water faucet allows air into the tank to replace the water that is being drained. This prevents a vacuum from forming. It is imperative that the water heater be disconnected (electrically) at this point, as it is a big no-no to allow the heating elements to be exposed to air while in operation. (They will blow up.)
If you have a pump around that can hook up to a garden hose (or a similar pump with some thread adapters), you might want to connect it to the end of the garden hose to speed up this process.
Once the water heater is drained, close the drain valve and remove the bottom element. Take the cover plate off, take some pictures of the wiring to make sure you know later where things are supposed to go, and then remove the element. If you have a wet vac, attach a hose in there to suck out the remaining sediment. If it gets too thick, open the gate valve up top for 5 seconds to let more water in.
At this point, you can do it yourself or call a plumber (by this, I of course mean that you should call them, schedule an appointment, and do the stuff listed above 2 hours before they came.)
Put a new element in and wire it up. See this video: http://www.youtube.com/watch?v=pNntz_NVLfU .
Before refilling the water heater, you should check your anode rod. This will be a hex-shaped bolt head at the top, sometimes hidden underneath insulation. Undo the hex bolt, which will take a lot of effort. You'll need a socket and a breaker bar, as they are often incredibly difficult to remove. Once loosened, pull it up and inspect it. If it is down to a thin wire or nearly there (see this diagram: http://www.rvingoutpost.com/library/AnodeRodPic.jpg ), you need a new one. If there is a ceiling above the water heater, you'll have to pull it up, cut it with a hacksaw, pull it up more, cut again, repeating this process until it's removed. Just don't drop it back in the tank after you've cut the bolt head off. If you have ample clearance above the water heater, you can replace it with a solid, continuous anode rod, but if there's a ceiling, then they make flexible/sectioned ones like this: http://www.accentshopping.com/ImageGen.ashx?IMG_ID=24592 . Put some pipe dope or PTFE tape on the threads of the bolt head before putting it back in.
Now it's time to fill the water heater back up. Make sure the drain is close once again, and remove the garden hose. Close the hot water faucets and open up a shower faucet instead (the faucet, not the head,) making sure that it's set on 100% hot water. (A shower faucet is preferable to a sink faucet, as they do not have a aerator/screen that any of the stirred-up gunk can clog.) Once the water heater is full of water, you can plug it back in and turn off the shower faucet.
If it's a gas heater, I'll bet it's a broken dip tube.
There was a time, when all the dip tubes were made by a handful of suppliers...who most/all used a plastic that, as it turns out, deteriorates after soaking in water for ten years or so. So the problem, especially with older water heaters is pretty common.
So, if your water heater is "of a certain age" chances are you've got a broken or disintegrated dip tube and you need to replace it.
Depending on the clearance above your water heater, etc. you should be able to just slide out the old one and slip in the new one. You may not even have to drain the tank. (But you might want to flush out as many of the plastic bits as possible before the travel around your plumbing system and make trouble elsewhere.)
If you have a lot of minerals in your hot water tank they can build up and then your tank can be full of sediment. I have seen sand, clay, calcium all kinds of sediment in the bottom of hot water heaters. If you do have a high mineral content in your water then you should flush your hot water tank once in a while because this could cause that problem. When it build up then the how water tank has a hard time heating the water if you have gas then it has to heat that sediment up first so it takes longer to heat the water. Also it lowers the volume of water so you do not have the volume of hot water that you previously had.
The first thing to check is flush the tank to remove sediment that may be reducing hot water storage space. This flushing should be done every three years.
