First, narrow the problem. If only one fixture has no hot water, the fixture or its shutoff valve is the issue, not the heater. If the whole house lost hot water, the heater is the issue. From there, gas and electric heaters have different things to check and different "stop and call a pro" thresholds.
Quick checks
- Is it just one fixture, or the whole house?
- How old is the heater? Tank: 8 to 12 years is typical lifespan.
- Gas, electric, or tankless?
- Is anyone smelling gas, hearing leaks, or seeing water around the heater?
- Recent power outage, breaker trip, or thermostat change?
- For tankless: did the heater throw an error code on the front display?
If only one fixture is cold
Check the fixture's hot water shutoff valve. Many sink fixtures and toilets have a valve under the cabinet. The faucet itself may have a cartridge or anti-scald limiter problem. Showers commonly have an anti-scald valve that drifts over time. This is a fixture problem, not a water heater problem.
Gas water heater: step by step
- Check the gas supply. Make sure the gas shutoff at the heater (and at the meter, if you can see it) is on. If your kitchen stove or other gas appliance also has no gas, the utility is the call, not the heater.
- Look at the pilot or ignitor. Older standing-pilot heaters have a small viewport. If the pilot is out, follow the heater's printed instructions on the label to relight. If it won't stay lit or you smell gas, stop and call a plumber. Don't keep trying.
- Check the gas control valve. The thermostat dial should be set to a normal temperature (around 120°F). If the temperature dial is at "Vacation" or "Pilot only," the burner won't fire.
- Newer electronic-ignition heaters often show a status light or error code. Match it against the label on the cabinet door.
- If the pilot is lit, the gas valve is on, and the dial is normal but there's still no hot water, the thermocouple, gas valve, or burner has failed. That's a plumber call.
Electric water heater: step by step
- Check the breaker in the main electrical panel. A water heater breaker is usually a 30-amp double-pole. If tripped, switch it fully off and then back on. If it trips again, stop. A repeatedly tripping breaker means an electrical fault, not a setting.
- Check the high-temperature reset (ECO). Most electric heaters have a red reset button behind a panel on the upper thermostat. If it tripped, press it once. If it trips again, stop and call a plumber. A repeating ECO trip usually means a failed thermostat or heating element.
- Listen for the elements. An electric heater heating water makes a soft hum or hiss as the elements work. Total silence usually means no power getting to elements.
- If the breaker is on, the ECO doesn't trip, and the temperature dial is normal but there's still no hot water, one or both heating elements have likely failed. That's a service call.
Tankless water heater: step by step
- Check the front display for an error code. Note the exact code and match it against the manual.
- Reset the unit by cycling power at the breaker or unit switch. Many tankless errors clear with a reset.
- Check the gas supply and venting. Tankless units are picky about gas pressure. A recent gas appliance addition can starve a tankless of the gas it needs.
- Check the cold water inlet filter if your model has one and the manual walks you through it. A clogged inlet screen can stop the flow sensor from triggering ignition.
- For descaling-related issues on tankless units in hard water areas, see how often to descale a tankless water heater.
- Anything that doesn't reset cleanly goes to a plumber. Tankless units have more failure modes than tank heaters.
If the heater is making sounds but water is cold
Popping, rumbling, or hissing in a tank heater usually means sediment buildup. The burner or element is heating sediment instead of the water. Hot water output drops because the sediment insulates the water from the heat source. See water heater making popping noise.
If hot water is lukewarm but not cold
Different problem. Check whether the dip tube has failed (cold water mixes with hot at the top instead of being delivered to the bottom), whether the thermostat is set too low, or whether the tank is undersized for current demand. See hot water runs out too fast for the lukewarm and short-supply cases.
When to call a plumber now
- You smell gas at any point. Leave the house and call the gas utility from outside.
- The breaker repeatedly trips after a reset.
- The ECO reset button repeatedly trips after a reset.
- Water around the base of the heater.
- Heater is older than 10 to 12 years and hot water has stopped.
- Tankless error code that doesn't clear with a reset.
- Pilot won't stay lit after relighting per the manual.
Good maintenance rhythm
- Yearly: flush sediment from a tank heater per the manual.
- Every 3 to 5 years: have a plumber check the anode rod.
- Yearly for tankless: descale per the manual, especially in hard water areas.
- Monthly: glance at the base of the heater for any drips or rust.
- Yearly: confirm the temperature dial setting (120°F is the DOE recommendation for most households).
- After any power outage: confirm the electric heater's breaker is on and the ECO didn't trip.
- Track the install date and age so you can replace before failure, not after.