The clearest signs a water heater is going out are water at the base of the tank, rusty hot water, rumbling or popping when it heats, hot water that runs out sooner than it used to, and plain old age. Manufacturers commonly put the life of a tank water heater at around 8 to 12 years, and the Department of Energy's consumer guide says most last 10 to 15 years. Water quality, daily use and maintenance decide where yours lands.
One sign on its own doesn't always mean replacement: a noisy tank may just need flushing, and a puddle may be coming from a fitting.
Age, and how long water heaters last
Age changes how you read every other symptom. A 4-year-old heater that stops making hot water probably needs a part. A 13-year-old heater with the same problem is a candidate for replacement, because parts for a tank that may leak next year rarely pay off.
If the install date isn't written on the tank, the manufacture date is coded into the serial number on the rating plate. The format varies by brand: some use letters for the month and year, others digits for the year and week. The manufacturer's website or support line can decode it in a minute.
Rusty or discolored hot water
Rusty hot water can come from two very different places. Run the cold water at the same faucet. If the cold is clear and only the hot is discolored, the rust is most likely coming from inside the water heater. If both are discolored, look instead at old galvanized steel piping or recent work on the water main in your street; the heater may be fine.
Inside the tank, the steel is protected by a glass lining and an anode rod, a metal rod designed to corrode so the tank doesn't. Once the anode is used up, the tank starts to rust. Replacing the anode on a younger heater can extend its life, but once an older tank is putting out rusty water, the corrosion is usually too far along for that to help.
Rumbling, popping or crackling noises
A water heater making popping noises is almost always dealing with sediment. Minerals settle to the bottom of the tank over the years. On a gas heater the burner sits right under that layer, and water trapped beneath it flashes to steam: that's the popping or rumbling. Electric heaters tend to hiss instead, as scale coats the elements.
Sediment wastes energy and can make the bottom of the tank run hotter than it should. Draining a little water regularly helps; the Department of Energy's Energy Saver guide suggests a quart every three months, following the manufacturer's directions. The catch is an older tank that has never been flushed: opening a long-closed drain valve can stir up enough sediment that it won't seal again. On a heater that's loud and past ten years old, the noise often means the tank is near the end.
Water at the base of the tank
Before you assume the worst about a puddle, dry the floor and check each of these:
- The pipe connections on top. A drip at a fitting can run down the side of the tank and look just like a tank leak. White or green crust or rust streaks around the connections point here.
- The drain valve near the bottom, which may weep or not be fully closed.
- The relief valve discharge pipe running down the side. Water at its end means the T&P valve has opened (more on that below).
- Nearby equipment. A furnace, air conditioner or boiler drain line can leak onto the same spot.
Gas heaters add one harmless source: when a tank full of cold water fires up, combustion moisture can condense and drip onto the burner with a sizzle until the water heats.
If none of that explains it and water is seeping from under the jacket or the bottom of the tank itself, the inner tank has corroded through. A water heater leaking from the bottom like this can't be repaired, and these leaks tend to get worse, sometimes suddenly.
What to do if your water heater is leaking
- If you smell gas near the heater, don't touch any switches. Leave the house and call the gas company or 911 from outside.
- Shut off the cold water supply at the valve on the cold line above the heater. Turn a round handle clockwise until it stops; turn a lever a quarter turn so it sits across the pipe.
- Shut off the energy source. On a gas heater, turn the gas control knob to Off. On an electric heater, switch off its breaker, but only if you can reach the panel without standing in water.
- Open a hot water faucet somewhere in the house to relieve pressure in the tank.
- Move belongings away from the water. Once the supply is off, a slow leak can usually wait for the technician.
A relief valve that drips or discharges
The T&P (temperature and pressure relief) valve is the brass valve near the top of the tank with a pipe running toward the floor. It's a safety device: if the water gets too hot or the pressure too high, it opens so the tank can't rupture. Never cap, plug or remove the discharge pipe to stop a drip.
A valve that drips now and then may simply be worn, and it can be replaced. Often, though, pressure is climbing. Water expands as it heats, and in homes with a check valve or pressure-reducing valve on the main water line, that extra volume has nowhere to go without a thermal expansion tank. High incoming pressure or a temperature set too high can do it too. A valve that dumps a lot of hot water is more serious: shut off the heater's gas or power and have it checked before using it again.
Running out of hot water, or temperature swings
If showers turn lukewarm sooner than they used to, the cause depends on the fuel. Electric heaters have two elements, and when the lower one fails the heater still makes some hot water, just much less. Elements and thermostats are replaceable, so on a heater that isn't old, this is usually a repair.
On gas heaters, a thick sediment layer takes up room and insulates the water from the burner. With either fuel, a broken dip tube (the pipe that carries cold water to the bottom of the tank) lets cold water mix in at the top. And sometimes nothing is broken: the household grew, and the heater is simply too small now.
Water that swings between scalding and lukewarm points to a thermostat or gas control problem, or a worn mixing valve in the shower itself. Have it checked, since scalding water is a hazard on its own.
A pilot or burner that won't stay lit
A pilot that keeps going out, or a burner that lights and then shuts down, can come from a worn thermocouple or flame sensor, a clogged air intake screen at the base, or a tripped safety sensor near the combustion chamber. Most are reasonable repairs on a younger heater.
It can also be a venting problem, which is a safety issue. If the flue is blocked, or the chimney no longer drafts well (which can happen after a furnace or boiler that shared it is replaced with one venting out the side wall), combustion gases, including carbon monoxide, can spill into the basement. Soot or scorch marks around the top of the heater are a warning sign. Have it inspected rather than relighting it over and over, and if your carbon monoxide alarm sounds, get everyone out and call 911. Our guide to carbon monoxide warning signs covers what to watch for.
A rotten egg smell from the hot water
If the hot water smells like sulfur but the cold doesn't, the cause is usually inside the tank. Sulfate-reducing bacteria in the water react with hydrogen produced by the anode rod and give off hydrogen sulfide. It's more common with well water. It doesn't mean the heater is failing; swapping the anode for a different type and disinfecting the tank usually fixes it.
A rotten egg smell in the air around a gas water heater is a different matter. Natural gas and propane are given that odor on purpose so leaks get noticed. Don't operate any switches; leave the house and call the gas company or 911 from outside.
Your replacement options
If the signs point to replacement, decide before the tank fails rather than after, when the choice narrows to whatever can be installed that day.
Gas tank. The most familiar choice and usually the simplest swap if you already have gas and a sound vent. It recovers quickly, so back-to-back showers aren't a problem. The main question is venting, especially if the heating system that shared its chimney has changed.
Electric tank. The lowest upfront cost and no venting, but slower recovery than gas and higher running costs than a heat pump model.
Heat pump water heater. A tank with a small heat pump on top that pulls heat from the surrounding air. The Department of Energy says they can be two to three times more energy efficient than conventional electric water heaters. They need room to breathe: ENERGY STAR calls for an indoor space that stays between 40°F and 90°F year-round with about 1,000 cubic feet of air around the unit. They cool and dehumidify the space they're in, need a condensate drain and make some fan noise. For 2026 installations, Mass Save lists a $750 rebate on qualifying ENERGY STAR models that replace an existing electric, propane, gas or oil water heater. Eligibility depends on your utility, so if your electricity comes from a municipal light plant, as it does in Concord, Hudson and Wellesley, check with that utility too.
Tankless. Heats water only as it flows, so it doesn't run out the way a tank does, though it can only supply so many fixtures at once. It takes little space and typically outlasts a tank. The trade-offs are cost and installation: gas models usually need a larger gas line and new venting, electric ones need substantial electrical capacity, and hard water means periodic descaling.
Many Massachusetts homes with a boiler don't have a separate water heater at all. The boiler either heats water through a coil inside it (a tankless coil), which keeps it hot all summer just for showers, or feeds an indirect tank that it heats like another zone. Then a hot water problem is really a boiler question, which our boiler replacement page covers.
When comparing prices, check that every quote includes venting changes, an expansion tank if needed, permits and haul-away. Our guide on how to compare HVAC quotes walks through what to look for.
If your water heater shows more than one of these signs, or it's past ten years and you'd rather replace it on your schedule than after a leak, our water heater replacement page explains how a visit works. You'll have the price before any work starts.
Sources: Rheem; A. O. Smith; U.S. Department of Energy, Energy Saver Guide (PDF); ENERGY STAR, Heat Pump Water Heaters; Mass Save, Heat Pump Water Heater Rebates; Bradford White.