No hot water? How to troubleshoot your water heater
Quick answer
Three different problems get lumped together: no hot water at all, hot water that runs out fast, and lukewarm water — each has its own causes. On a gas heater, no hot water usually means the pilot is out or the thermocouple failed. On an electric heater, check the breaker and press the red high-limit reset button on the upper thermostat. Water that runs out quickly often means sediment buildup, a broken dip tube, or a failing heating element.
Common causes
- Gas: a pilot light that's gone out, a failed thermocouple, or no gas supply.
- Electric: a tripped breaker, a tripped high-limit reset, or a failed heating element/thermostat.
- Runs out fast: sediment buildup reducing capacity, a broken dip tube, or one failed element of two.
- Lukewarm: a thermostat set too low or a partially failed element.
- An undersized heater for the household's demand.
What to check first
- Is it gas or electric? That decides where to look.
- Gas: check whether the pilot is lit and relight it following the label instructions.
- Electric: check the breaker, then press the red reset button on the upper thermostat behind the access panel.
- Confirm the thermostat is set around 120°F (not turned down).
- Note the symptom — none vs. runs out fast vs. lukewarm — because each points somewhere different.
When it's urgent
If you ever smell gas, leave and call your gas utility from outside — don't relight anything. Water that's suddenly scalding can mean a stuck thermostat — turn it down. And if the tank itself is leaking, that's a separate, time-sensitive problem (see our water-heater leak guide).
DIY vs. call a pro
You can likely DIY
- Relighting a gas pilot per the manufacturer's steps.
- Resetting the breaker and the high-limit button on an electric unit.
- Adjusting the thermostat and flushing sediment from the tank.
Call a pro for
- Replacing a thermocouple, gas control valve, heating element, or thermostat.
- A pilot that won't stay lit or a breaker that keeps tripping.
- Recurring failures or sizing problems.
Estimated cost range
How HouseCue helps
HouseCue is a private, homeowner-first app that turns this from a one-time worry into a tracked plan. Snap a photo for an AI diagnosis, upload your inspection report to auto-build a handbook, and get seasonal reminders for your roof, HVAC, water heater, plumbing, and electrical — so nothing slips. Connecting with a pro is always optional and only when you choose.
Get started freeFrequently asked questions
Why do I suddenly have no hot water?
On a gas heater, the pilot light likely went out or the thermocouple failed. On an electric heater, a tripped breaker or a tripped high-limit reset is the usual cause. Relight the pilot or reset the breaker/high-limit button; if it won't stay lit or keeps tripping, call a pro.
Why does my hot water run out so fast?
Common causes are sediment buildup that's shrinking the tank's effective capacity, a broken dip tube mixing cold water into the hot outlet, or (on electric units) one of two heating elements failing. Flushing the tank helps with sediment; element and dip-tube issues need parts.
Where is the reset button on an electric water heater?
It's a red button on the upper thermostat, behind the access panel and insulation on the side of the tank. If it's tripped, pressing it can restore heat — but if it trips again, there's an underlying fault (often a failing element or thermostat) that needs service.
Related guides
HouseCue guides are general educational information, not professional inspection, engineering, or contracting advice. Costs vary by market. For safety issues — gas, electrical, structural, or major water — contact a qualified professional.