No Hot Water? How to Find the Cause by Water Heater Type
No hot water almost always traces to one failed part, and which part depends on whether your heater is gas, electric, or tankless. On electric, suspect a tripped breaker, a popped reset button, or a burned-out heating element. On gas, suspect a dead pilot light, a bad thermocouple, or the gas valve. On tankless, suspect flow, gas supply, or an error code. Work the checks below in order before you call anyone.
First, rule out the fast stuff (60-second triage)
Before you open a panel, confirm the problem is the heater and not the tap or the timing. A full tank of hot water is a finite supply, and a long shower or two can empty it. If the water was hot an hour ago and is cold now, run this quick triage first. It clears the most common false alarms.
- Open a hot tap and let it run 60 seconds. Warm-then-cold means you drained the tank and it is reheating, not broken.
- Check a second faucet. If one fixture is cold but others are hot, the fault is that fixture, not the heater.
- Confirm the heater has power (electric) or a flame or igniter (gas). No power and no flame is your answer.
- Note the thermostat setting. Most tanks ship at 120 degrees F; a knob bumped to “vacation” or low will feel lukewarm.
- Wait one recovery cycle: about 30 to 40 minutes for gas, 60 to 90 minutes for electric, before assuming failure.
Symptom-to-cause table by heater type
Use the pattern of the symptom to narrow the cause fast. Cold water that never warms points to power, gas, or ignition. Water that runs out quickly points to a single failed element or sediment. Lukewarm-only points to a thermostat or a partial element failure. Match your symptom to the likely cause and fix below.
| Symptom | Heater type | Likely cause | First fix to try |
|---|---|---|---|
| Completely cold, no warmth | Electric | Tripped breaker or popped reset button | Reset breaker; press red reset button on upper thermostat |
| Completely cold, no warmth | Gas | Pilot out or dead thermocouple | Relight pilot per the tank label; replace thermocouple if it will not stay lit |
| Completely cold, no warmth | Tankless | No flow signal, gas off, or ignition fault | Check gas valve on, clean inlet filter, read the error code |
| Runs hot then cold in minutes | Electric | Lower heating element or lower thermostat failed | Test elements with a multimeter; replace the dead one |
| Runs out faster than it used to | Gas or electric | Sediment buildup cutting capacity | Flush the tank; annual flushing prevents it |
| Lukewarm only, never hot | Electric | Upper thermostat set low or one element out | Raise thermostat to 120 F; test upper element |
| Lukewarm only, never hot | Gas | Weak burner flame or partial gas restriction | Check gas valve fully open; call a pro for burner service |
| Cold burst mid-shower | Tankless | “Cold water sandwich” or low gas pressure | Steady the flow; a plumber checks gas sizing |
| Error code on display | Tankless | Ignition, flame, or temperature fault | Look up the code (see below) and clear or call a pro |
Gas water heater: pilot, thermocouple, and gas valve
On a gas tank with no hot water, the flame is out. The three usual culprits are a pilot light that blew out, a failed thermocouple that shuts the gas off as a safety measure, and the gas control valve itself. Check them in that order, and stop immediately if you smell gas.
Safety first: if you smell rotten eggs or sulfur near the heater, do not touch any switch, thermostat, or flame. Leave the house and call your gas utility from outside. That smell is the odorant added to natural gas and propane, and it means a possible leak, not a relight job.
- Look through the sight glass or lower access cover. If the pilot flame is out, relight it following the printed steps on the tank, which usually means setting the knob to “pilot,” holding it down, and sparking the igniter.
- If the pilot lights but dies when you release the knob, the thermocouple has likely failed. This sensor tells the valve the flame is present; when it dies, it cuts the gas. A plumber replaces it in under an hour on most tanks.
- Confirm the gas control valve is set to “on,” not “pilot” or “off.” A bumped valve is a common no-heat cause.
- If the pilot and thermocouple are fine but the burner will not fire, the gas valve or thermostat inside it may have failed. That is a professional replacement, not a DIY fix.
Electric water heater: breaker, reset button, and elements
On an electric tank, no hot water means no heat is reaching the water. Start at the panel, then the safety reset, then the heating elements. Most electric tanks have two elements and two thermostats, so a single dead lower element often shows up as hot water that runs out fast rather than a fully cold tank.
- Check the circuit breaker. A tripped double-pole breaker feeding the heater is the single most common cause. Flip it fully off, then on.
- Turn the breaker off, remove the upper access panel, and pull back the insulation to find the red reset button on the thermostat. Press it until it clicks. This high-temperature cutout trips when water overheats.
- Restore power and wait 60 to 90 minutes for a full reheat before judging the result.
- If the tank is still cold, kill the power and test both heating elements with a multimeter for continuity. A reading near zero means a good element; no reading means a burned-out element to replace.
- If the reset button trips again after you press it, stop. Repeated tripping means a shorted element or a failing thermostat, and continuing risks the tank overheating.
Tankless water heater: flow, gas, and error codes
A tankless heater only fires when it senses enough water flowing, so “no hot water” here often means it never turned on. It needs a minimum flow, usually around 0.5 gallons per minute, plus adequate gas and a clear ignition path. Most gas tankless units show an error code that names the fault, which makes diagnosis faster than any tank.
- Confirm the gas is on at the unit and the meter, and that no other gas appliance recently lost supply.
- Clean the cold-water inlet filter and open the shutoff valve fully. A clogged screen or half-closed valve starves the flow sensor and the unit never ignites.
- Read the display. A code narrows it instantly. On Noritz units, for example, code 11 is ignition failure (no spark, air, or gas), code 12 is flame loss after ignition, and code 90 is a temperature failure after repeated attempts. Other brands use their own numbers, so check your manual.
- Descale the heat exchanger if you have hard water and have not flushed it in over a year. Mineral scale chokes output and drives fault codes.
- If the unit shows an ignition or combustion code that returns after a reset, book a pro. Gas pressure and venting faults are not DIY territory.
When to call a plumber
Call a professional when the fix involves gas components, electrical faults that keep tripping, or a tank that is leaking. These carry real safety and water-damage risk, and several are code-regulated. A licensed plumber can also tell you whether a repair is worth it or whether replacement is the smarter spend on an aging tank.
- Any gas smell, or a pilot and thermocouple that will not hold a flame after relighting.
- An electric reset button that trips repeatedly, which points to a shorted element or bad thermostat.
- Water pooling under the tank, which usually means a corroded tank that cannot be repaired.
- A tankless error code that returns after cleaning and resetting, especially ignition or gas-pressure faults.
- A heater over 10 years old that needs a major part. Weigh the repair against the cost to replace a water heater before spending on it.
If you do replace the unit, note that installs are permit-and-inspection work in most areas, and the water heater code requirements for expansion tanks, T&P valves, drip pans, and venting vary by state and local code. When the job crosses into gas or electrical work, hire a licensed plumber near you rather than risking a code violation or a safety hazard.
Frequently asked questions
What is the first thing to check when there is no hot water?
Check whether the water heater has power or a lit flame. On an electric unit, look at the circuit breaker and the red reset button behind the upper panel. On a gas unit, check that the pilot or igniter is working and the gas valve is on. These two checks solve most no-hot-water calls before any parts get replaced.
Why do I suddenly have no hot water?
A sudden loss usually means a single failure: a tripped breaker or reset switch on electric, a pilot light or thermocouple that quit on gas, or a flow or ignition fault on tankless. Sudden total loss points to power, gas, or a safety cutout, not sediment, which builds slowly. Start with the breaker or the flame.
How long does a water heater take to reheat?
A gas tank reheats a full tank in about 30 to 40 minutes; an electric tank takes 60 to 90 minutes. If you drained the tank with long showers, the water may be cold simply because it has not caught up. Wait one recovery cycle before assuming the unit failed. A tankless heater delivers hot water within seconds when it fires.
How do I reset an electric water heater?
Turn off the breaker feeding the heater. Remove the upper access panel and pull back the insulation to find the red reset button on the thermostat. Press it firmly until it clicks. Replace the panel, restore the breaker, and wait 60 to 90 minutes. If the button trips again, stop and call a plumber, because it signals an overheating fault.
Is it safe to relight a gas water heater pilot myself?
Relighting a pilot is homeowner-safe if you follow the label on the tank and smell no gas. If you smell rotten eggs or sulfur, do not touch any switch or flame. Leave the house, then call your gas utility from outside. A pilot that will not stay lit usually means a failed thermocouple, which a plumber replaces.
Last reviewed: August 2026.