No hot water is one of the most common calls we get, and a fair number of them have a simple cause you can check in a few minutes. This guide walks through what to look at first, depending on whether you have a gas, electric, or tankless water heater, and when it's time to call a professional.
Smell gas? Stop here. Don't touch light switches or try to relight anything. Leave the house and call PG&E or 911 from outside.
First, Narrow It Down
Two quick questions point you toward the cause:
- Is there no hot water anywhere, or only at one faucet? If it's one fixture, the problem is probably that fixture's mixing valve or cartridge, not the water heater.
- Is there no hot water at all, or not enough? Hot water that runs out quickly or is only lukewarm has different causes than none at all. We cover both below.
Gas Water Heater: No Hot Water
Check the pilot light
Most gas tanks have a small viewing window near the bottom. If you don't see a flame, the pilot has gone out. Many units have relighting instructions on a label on the tank; our pilot light relighting guide walks through the usual steps. If the pilot lights but goes out again when you let go of the button, the thermocouple or flame sensor has most likely failed. That's a quick, routine repair.
Check the gas supply
Make sure the gas valve on the line to the heater is open (handle parallel to the pipe) and that other gas appliances, like the stove, are working. If nothing gas works, the issue is the supply, not the heater.
Newer models need power too
Many newer gas water heaters, including power-vent units and those with electronic ignition, plug into an outlet. Check that it's plugged in and the outlet or GFCI hasn't tripped.
Electric Water Heater: No Hot Water
Check the breaker
Electric water heaters run on a dedicated 240-volt breaker. If it has tripped, reset it once. If it trips again, stop and call a professional. Something is shorting.
Check the high-limit reset
Behind the upper access panel on most electric tanks is a red reset button on the high-limit thermostat. With the power off at the breaker, you can remove the cover and press it. If it clicks and the heater works again, it tripped for a reason, often a failing thermostat or element, so have it checked if it happens again.
Failed element or thermostat
If the breaker and reset are fine, the most likely cause is a burned-out heating element or a failed thermostat. Electric tanks have two elements, and when the upper one fails you usually get no hot water at all. These are standard element and thermostat repairs.
Tankless Water Heater: No Hot Water
- Read the error code on the display. It usually narrows the problem to ignition, flame, flow, venting, or overheating.
- Check the gas and power supply. Tankless units need both.
- Run more water. Tankless units need a minimum flow rate to fire. A single faucet barely open may not be enough.
- Think about scale. In hard water, a scaled heat exchanger or clogged inlet filter can cause shutdowns. Our guide to common tankless problems covers this in detail.
Hot Water Runs Out Fast or Is Lukewarm
- Sediment buildup. In Brentwood's hard water, sediment can fill the bottom of a tank and take up space meant for hot water. If the heater rumbles or pops, a flush may help.
- Broken dip tube. The tube that sends cold water to the bottom of the tank can crack, mixing cold water into the hot at the top.
- Thermostat set too low. Check the setting. Around 120°F is typical; see our water heater temperature guide.
- Failed lower element (electric). You get some hot water, but it runs out fast.
- The heater is undersized for your household. This is common after a family grows or a bathroom is added.
When to Call a Professional
Call for help if:
- The pilot won't stay lit after relighting.
- The breaker trips again after one reset.
- You see water around the base of the heater.
- The relief valve is discharging.
- You smell gas or see soot or scorching near the burner.
- You're not comfortable working around gas or 240-volt wiring.
We offer same-day water heater repair across Brentwood and East Contra Costa, and 24/7 emergency service when you're without hot water. If the heater turns out to be at the end of its life, our repair or replace guide explains how to decide.
Frequently Asked Questions
Why is there suddenly no hot water in my house?
On a gas heater, the most common causes are a pilot that has gone out or a failed thermocouple. On an electric heater, it's usually a tripped breaker, a tripped high-limit reset, or a failed upper heating element.
Why does my pilot light keep going out?
Usually a worn thermocouple or flame sensor that no longer senses the flame. A dirty pilot assembly, a draft, or poor combustion air in a closet can also cause it.
Should I reset my water heater?
You can reset a tripped breaker once, and press the high-limit reset on an electric tank with the power off. If either trips again, there's an underlying problem that needs a technician.
Why do I have hot water in one bathroom but not another?
If the water heater is supplying hot water elsewhere, the problem is likely the shower or faucet valve in that bathroom, not the heater.
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