Quick answer: No hot water usually comes down to a few things — for gas heaters it’s most often a pilot light or thermocouple; for electric it’s usually a tripped breaker or a failed heating element/thermostat. If you have some hot water that runs out fast, the tank is undersized or a heating element has failed. Start with the simple checks below before calling anyone.
Narrowing it down: thermostat or element?
Only the shower is lukewarm and the sinks are hot? Check the shower valve’s limit stop before the water heater: see shower not hot enough.
On an electric heater, a dead element is the usual culprit — see which element failed and what to buy.
Losing hot water is one of the most common plumbing problems, and a good share of cases are fixes a homeowner could’ve made in five minutes. Here’s how to diagnose it like a plumber, in order.
If the heater turns out to be undersized, our Water Heater Size Calculator shows what capacity your home needs.
First: gas or electric?
The cause and the fix differ by fuel type. Check the unit (or the breaker panel) and work the matching column.
| Symptom | Gas heater — likely cause | Electric heater — likely cause |
|---|---|---|
| No hot water at all | Pilot light out / bad thermocouple / gas supply | Tripped breaker / failed upper element or thermostat |
| Runs out fast | Undersized tank / sediment buildup / dip tube | Failed lower heating element / sediment |
| Lukewarm only | Thermostat set low / partial element issue | One of two elements failed / thermostat |
| Discolored or smelly | Sediment or anode rod — see hard-water note below | |
The homeowner checks (do these first)
- Check the thermostat setting. It should be around 120°F. Someone may have bumped it down. Free fix.
- Electric: check the breaker. A water-heater breaker that’s tripped is the #1 electric cause. Flip it fully off, then on. If it trips again, you likely have a failed element — stop and call a pro.
- Gas: check the pilot light. If it’s out, relight per the label on the tank. If it won’t stay lit, the thermocouple is usually the culprit (a small part, but a pro job for most). Many heaters with a status light on the gas valve run on a thermopile instead; see thermocouple vs thermopile vs flame sensor.
- Check the unit’s age. Tanks last ~8–12 years. If yours is older and failing, you’re likely replacing it, not repairing it. Replacement cost breakdown →
- Listen for popping/rumbling. That’s sediment. Flushing the tank can restore capacity and is good annual maintenance — especially in hard-water areas. Hard water signs & fixes →
“Some hot water but it runs out fast”
This is almost always one of two things: sediment taking up tank volume, or a failed heating element (electric — the lower element commonly fails first, cutting your capacity roughly in half). Flushing helps with sediment; a failed element needs replacing. If the tank is near end-of-life, replacement is the better spend.
Pulling an element yourself takes a 1-1/2 inch socket, not a standard one. See the best water heater element wrench.
When to call a pro
Call someone if: the breaker keeps tripping, you smell gas (leave first, then call), the pilot won’t stay lit after relighting, or there’s water pooling at the base of the tank (a leaking tank is a replacement, not a repair). Anything involving gas or the tank itself is pro territory.
Repair or replace?
If the unit is under ~8 years old and it’s a single failed part (element, thermostat, thermocouple), repair. If it’s older, leaking, or you’re tired of the capacity, replace — and use it as the moment to right-size and pick the better type — including tankless. Tank vs tankless → · Gas vs electric → · Best water heaters →
Relief valve dripping after a heating cycle? That is usually thermal expansion — see expansion tanks.
Frequently asked questions
Why do I suddenly have no hot water?
For electric heaters, a tripped breaker or failed heating element is most common; for gas, a pilot light that’s gone out or a bad thermocouple. Check the breaker or pilot first.
Why does my hot water run out so fast?
Usually sediment reducing tank capacity or a failed lower heating element (electric). Flushing helps sediment; a failed element needs replacement.
What temperature should my water heater be set to?
About 120°F — hot enough for the home, safe against scalding, and efficient. Many “no hot water” calls are just a thermostat bumped down.
Is a leaking water heater repairable?
If the tank itself is leaking, no — that’s a replacement. Leaks at fittings or the valve can sometimes be repaired.
Related: Water heater repair cost
Seeing water pooling under the tank too? Pin down the source with water heater leaking from the bottom.
If you have a gas heater and the pilot light will not stay lit, that is almost always a failing thermocouple, a simple DIY fix.
Seeing water on top of the heater instead of no hot water? See water heater leaking from the top.
Related: if you spot water around the unit, see why your water heater is leaking and how to fix it.
Related: hot water that runs out fast with nothing else wrong is often a broken dip tube — especially if plastic flecks keep turning up in the aerators.