Leaks, rust-colored hot water, new noises or reduced hot water warrant inspection; age adds context but does not diagnose failure. If you smell gas, leave immediately and call from outside. For an active water leak, isolate the heater only if safe. A discharging relief valve needs prompt assessment, never plugging.
Which signs mean shut it off right now?
Three signs mean act immediately: water leaking from the tank itself, a gas smell near a gas heater, and a temperature and pressure (T&P) relief valve that is discharging. Other symptoms usually call for a service appointment, but worsening leaks, unsafe wiring or a CO alarm need immediate action.
A gas smell. Southwest Gas says to leave immediately if you suspect a leak. From a safe place, call 911 and Southwest Gas at 877-860-6020. Don't touch switches, don't use a lighter, and don't stop to shut off the heater. Leave first. Our page on a house that smells like gas covers the rest.
Water coming from the tank body. A. O. Smith's installation manual states it flatly: "All water heaters eventually leak." If there is no gas smell, shut the heater down in this order:
- 1Close the cold water shutoff valve on the pipe feeding the heater. A. O. Smith tells installers to put one close to the heater and says to know where it is and how to shut off the water to the heater.
- 2On an electric heater, turn off its breaker. Rheem's electric manual says to turn off the circuit breaker if the heater has been subjected to physical damage or flood, among other conditions.
- 3On a gas heater, turn off the manual gas shutoff valve on the supply line to the appliance.
- 4Call a plumber.
Our page on a water heater leaking from the bottom helps you tell a failed tank from a loose fitting or a valve drip.
A relief valve that is discharging. Watts, which makes T&P valves, says: "Discharge from a T&P valve may indicate an unsafe temperature or pressure condition exists, which requires immediate attention by a qualified service technician or licensed plumbing contractor." See what a leaking pressure relief valve means. Never cap or plug the discharge pipe.
Which signs mean schedule a plumber this week?
These are the early warnings. None is an emergency alone, but each points to a problem that grows.
| Sign | Usual cause | What to do |
|---|---|---|
| Rust-colored hot water | Corrosion in the tank or fittings | Check if cold water is rusty too, then book an inspection |
| Popping or rumbling | Sediment on the tank bottom | Flush the tank, then recheck |
| Hot water runs out sooner | Sediment, or a failed element or thermostat | Diagnose before replacing |
| Pilot keeps going out (gas) | A failing safety part or gas control | Stop relighting it and get it checked |
| Breaker keeps tripping (electric) | An element or wiring fault | Leave it off and get it tested |
Rusty hot water. Rheem lists rust-colored water among signs where replacement "is often the most economical solution." If only the hot side is rusty, the tank is the likely source. Rust on the cold side can also involve the supply or house piping; replacing the heater alone may not solve it. Hot water that smells like rotten eggs is a different issue. A. O. Smith ties it to the anode rod, sulfate in the supply water and a bacteria it calls harmless. Our page on smelly hot water walks through it.
Popping and rumbling. Rheem says that if a heater is "rumbling, popping, or cracking during operation, sediment buildup is usually the culprit." A. O. Smith's manual points owners to its flushing instructions for the same sounds. Phoenix water is very hard, so sediment builds faster here, and flushing a water heater in Phoenix is worth doing on a schedule. More on the noise in why a water heater pops or rumbles.
Less hot water. Rheem notes that heavy sediment "may reduce the amount of usable hot water in a tank system." On an electric heater, a burned-out element can do the same. See why you run out of hot water so fast.
Pilot and breaker trouble. A pilot that won't stay lit is a symptom, and relighting it over and over hides the cause. See a pilot light that won't stay lit. On an electric unit, don't keep resetting a tripping breaker. See why an electric water heater keeps tripping the breaker.
How old is too old for a water heater?
About 10 years is when to start planning. Rheem states: "Most conventional tank water heaters last around 10 years." It recommends planning replacement around year 10 rather than waiting for an emergency. Water quality, flushing habits and anode rod condition move a real unit to either side of that number.
The rating plate on the heater carries the model and serial number, and the serial number usually encodes the build date. Age plus any warning sign is a stronger case for replacement than the sign alone. An older tank with rusty water deserves a condition assessment. A younger noisy tank may need sediment service, but age and sound alone do not identify the failed part.
Repair or replace: how do you decide?
A failed part on a younger tank is a repair. Internal corrosion or a body leak is a replacement.
- Repair: a tank under about 10 years old with a bad thermostat, element or gas control, or sediment noise that clears after a flush.
- Assess replacement: a confirmed leak or failed tank body generally requires replacement. Investigate rusty hot water first; anode condition, connections, supply piping and tank corrosion can have different remedies. Age and repeat failures help compare repair cost with replacement, but are not a diagnosis.
- Check the warranty first: the model and serial number tell the manufacturer what applies, and a tank failure on a young heater may be covered.
Our page on whether to repair or replace a water heater goes deeper, and checking for a recall takes minutes with the model number in hand. If you replace it, see the Phoenix permit rules for water heater replacement.
What can you do while you wait?
If the heater is not leaking and there is no gas smell, you can keep using it until service. If it is leaking, keep the water and power or gas off. A. O. Smith advises a metal drain pan under the heater, which is worth having wherever a leak could damage the house. Not sure whether what you see is urgent? When to call an emergency plumber draws the line. HQ is licensed and insured, and gives free estimates and upfront pricing before work starts.