Usually, a hot water heater doesn't fail without first giving some indications that it's reaching the end of its functional life. But how do you know exactly when it's on its last leg (or when you simply need water heater repair)?
Visible rust, leaks coming from the water heater itself, and water temperatures that no longer seem hot enough are all signs that it may be time for a full-on water heater replacement. Age is a good indicator as well. If your appliance is from the previous century, it's probably time to replace it with a new water heater.
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1. Visible Corrosion on the Heater
Rusty areas on the outside of the hot water heater usually mean it's corroded inside too. In normal indoor conditions in a space that's not too damp, there are no external factors that should cause a water heater to rust or corrode on the outside. Hot water heaters generally have an inner tank that holds the water and then an outer tank or shell that insulates the inside to help keep the water hot. The outer tank won't usually rust unless the inside tank is cracked and leaking.
If the inner tank is leaking enough to cause the outer tank to rust, that means it's been leaking for a while, and the problem should not be ignored. At any time, the entire hot water heater can rupture, so it's best to replace it as soon as possible before this occurs.
In rare circumstances, such as an overly damp basement or a room exposed to floodwaters, there's a chance the outside of the hot water heater could show rust spots even if the inner tank is still in good shape. If the water heater seems to be functioning properly, isn't very old, and you have reason to believe external circumstances caused the rust, a few specks of surface rust might not be a major concern.
2. Water Leaks From the Tank
Water leaking from the hot water tank usually means one of two things: Either there's a faulty connection where a pipe or other element connects to the tank or the tank itself has a crack or hole in it. A leak at a pipe connection or a valve is usually a simple fix that doesn't indicate anything wrong with the tank, but if the leak seems to emanate from the body of the tank away from any fittings, it's time to replace the tank as soon as possible.
If the leak seems to be coming from the top of the tank, it could be a loose valve or the water pipes leading in and out of the tank. If you or a professional plumber you hire tighten everything and the tank seems to leak from the body, it's most likely time to replace the tank. A leak coming from the bottom of the tank could be the drain valve, which means it needs to be tightened. If it's tight and the water is coming from the tank itself, the tank is cracked and needs to be replaced. If you can't figure it out, have a pro inspect the tank to determine the source of the leak, as an actual tank leak means it's time to replace the heater immediately.
An old anode rod in the tank could also cause the tank to leak if the rod corrodes to virtually nothing, and its fitting also corrodes. This sacrificial metal rod attracts minerals in the water to help prevent them from corroding the actual tank, but as it starts to fail, the water heater may not work as well as it used to. Replacing the rod every five years or so extends the life of the water tank, as it cuts down on the likelihood of the tank corroding and leaking.
3. Pilot Light Won't Stay Lit
A pilot light that won't stay lit for long isn't always a sign of a failing hot water tank, but it could be. If your hot water heater is less than 10 or so years old and the pilot light won't stay lit, a faulty thermocouple could be the culprit. This device controls gas flow to the burner, and if it goes bad, it could shut off the gas to both the burner and the pilot light. Thermocouples can be tested and repaired or replaced by a plumber.
In some cases, dust and debris are to blame for the pilot light frequently going out. The pilot light area needs oxygen from the air in order to function; all flames need air or they'll quickly go out. An accumulation of spiderwebs, dust, or chunks of rust from an old water tank could be to blame.
If your hot water heater is really old and the pilot light won't stay lit, there's a good chance the housing around it has rusted. Once this happens, it usually means there's more rust in the tank and that it's time to replace the entire tank. If you aren't sure, have a plumber inspect the pilot light assembly to determine whether it's fixable or replaceable or whether the tank itself needs to be replaced.
4. Hot Water Isn't Always Hot
If the hot water in your shower is scalding hot one day and lukewarm the next even though no one has used much hot water in the last few hours, this could indicate a problem with the hot water heater, especially if you've ensured the pilot light on your gas water heater is lit. There's a slight chance something is awry with the thermostat or that someone bumped or adjusted it. Turn the water heater's thermostat to a slightly higher temperature and run some hot water again after a couple hours. If the water still doesn't get warm enough, it could mean the dip tube inside the tank needs to be replaced; this is a fairly easy job for a plumber.
If neither the thermostat nor the pilot light is to blame for cooler than normal hot water in a gas water heater, the tank itself may be due for a replacement if it's more than five years old. The too-cool temperature could indicate a buildup of sediment, in which case flushing the tank may help. If there's too much sediment, the inner tank may be cracked, which means it's time to replace the old hot water heater as soon as possible. In an electric water heater, the issue could just be a broken heating element. A plumber can replace the heating element if that's the issue or determine if it's time to replace the entire hot water heater.
5. Strange Water Heater Noises
Pings, bangs, thunks, and rumbling sounds emanating from your hot water heater are indicators of mineral sediment accumulating inside the tank. While the sounds themselves don't mean your tank is about to fail, over time, too much sediment could cause the tank to leak. The more sediment, the less energy efficient the tank becomes as well. If your tank is noisy much of the time and doesn't work as well as it used to, it could be time to replace it, as too much time may have passed without flushing it. When there's too much sediment and it's been there quite a while, there's a good chance the heater is rusting inside and is on its way to developing a leak.
Flushing the tank periodically helps prevent some of the issues, as flushing the water out also removes some of the buildup and sediment. The key is to start flushing before sediment and mineral buildup become serious issues. It's a good idea to flush the tank once a year in a household with considerable hot water usage.
6. Cloudy or Discolored Water
Cloudy or discolored water is a common sign of sediment and minerals accumulating inside the hot water tank. If hot water coming from all the taps in your home looks somewhat yellow or brown but the cold water looks clear, it could be caused by rust in the hot water tank. Flushing the tank may temporarily get rid of the problem, but it can't stop rust from progressing. If the tank itself is rusty and old, it's time to replace it.
Note that oddly colored water isn't always a water heater issue. Rust-colored water often occurs when fire hydrants are tested nearby or during repairs to water lines in your area. This type of work could cause water from any tap or even from your hot water tank to appear rusty or brown for a while until you've run the water long enough to get the discolored water out of your home's pipes.
In most cases, the city sends out or posts notices ahead of working on water lines, but that's not always the case with fire hydrant testing. If you haven't noticed any such work going on in your neighborhood, call the local water or fire department to find out if they've done any work within a few blocks of your home.
Homes with galvanized steel pipes can get rusty water for other reasons. Shutting off the main water supply valve and turning it back on can give you rusty water for a while. The same thing can happen when you first start running water after being away from home for an extended period. In any case, if the rust doesn't go away quickly, the water heater tank becomes a suspect.
7. Age of the Tank
A hot water heater typically lasts eight to 15 years, but it could show signs of pending failure even earlier. Gas water heaters generally last eight to 12 years, and electric water heaters usually last 10 to 15 years, but if you're hearing strange sounds or sensing that the heater doesn't work as well as it used to, it may be time to replace it sooner than you think. To determine the age of your hot water heater, look for a tag featuring a serial number, which is usually a letter followed by a series of digits. The letter indicates the month, with A being January, B being February, and so on. The two following digits indicate the year of manufacture, so "C15" indicates March 2015.
Aging beyond its predicted life span doesn't always mean the water heater is due for failure, but if it's been in your home for a couple decades or since long before you moved in, it's a good idea to have it replaced or at least inspected to determine if all the replaceable parts and the tank itself are in good working order. Replacing it before it fails completely is better than dealing with no hot water for days on end or the tank splitting and flooding the house.
Keep in mind that if you call in a plumber and your tank is of a certain age (say, 10 years or older), the plumber is likely to say it's time for new water heater installation. A lot of pros won't even touch a heater past a certain age unless it's to remove it for replacement.
Tankless Water Heater Issues
Tankless water heaters last a little longer than conventional water heaters with tanks, but they aren't entirely immune to problems or failure. Mineral buildup is a major issue with tankless heaters, but this can be minimized by checking the filter regularly and by flushing the heater twice a year or so, especially if you live in an area with hard water. Leaks inside the heat exchanger eventually corrode the heater itself. As with the tank-style water heaters, a rusty tankless heater means it's time for replacement.
The electric igniter on the tankless heater may also fail at some point, preventing the heater from warming water. Dirt and debris or rust could keep the system from properly igniting. In many cases, the igniter can be replaced.
Tankless water heaters also have specialized venting and combustion systems that must remain clear in order for the heater to function. In most cases, an error code shows up on the heater indicating blocked airflow if there's an issue. Bird nests and other debris getting into the vents are responsible for these types of tankless heater malfunctions, but worse yet, the blockages could cause a fire hazard. In most cases, once the combustion and exhaust pipes are cleared, the heater should function normally again without any permanent harm to the heater.