One tap or all of them?
If only one faucet or shower runs cold, the problem is likely that fixture's valve or mixing cartridge, not the heater. If every tap is cold, go to the water heater.
Electric water heaters
- Check the breaker. If it tripped, reset it once. If it trips again, stop and call a pro.
- Many electric heaters have a high-limit reset button behind an access panel. Power must be off at the breaker before any panel is opened. If you're not comfortable, have a plumber do it.
- Heating elements and thermostats wear out. A plumber can test and replace them.
Gas water heaters
- Make sure the gas supply valve is open and other gas appliances work.
- Many newer heaters have an electronic igniter and a status light that flashes a code. The manual explains the code.
- If you smell gas, don't light anything or touch switches. Leave and call your gas utility from outside.
Hot water runs out fast
If you get some hot water but it runs out quickly, sediment build-up, a failed lower element on an electric heater or a heater that's too small for your household may be the cause. A plumber can flush the tank or size a replacement.