Short answer: First decide whether the problem is the whole house or one fixture. Whole house, electric heater: check the breaker and the high-limit reset, then suspect a failed element or thermostat. Whole house, gas heater: check that the gas is on and whether the pilot or igniter is working. One fixture only: the faucet cartridge or mixing valve. If you smell gas, leave and call the gas utility from outside.
Quick diagnosis
| What you notice | Most likely cause | What to check | Call a pro? |
|---|---|---|---|
| No hot water anywhere, electric heater | Tripped breaker, high-limit reset or failed element | Check the breaker | Often |
| No hot water anywhere, gas heater | Pilot out, gas supply off, failed thermocouple or igniter | Look at the pilot window and status light | Often |
| Some hot water but runs out fast | Sediment or one failed element | Listen for rumbling; note recovery time | Sometimes |
| Hot in the sink, not in the shower | Shower cartridge or mixing valve | Compare fixtures | Sometimes |
| Water heater leaking | Tank or valve problem | Look at the base and fittings | See leaking guide |
Electric water heaters
A. O. Smith lists a power issue or a faulty heating element among the causes of no hot water. Check the breaker first. Many electric heaters also have a high-limit (ECO) reset button behind an access panel; it trips when the water overheats. Because those panels expose live wiring, turn the breaker off before opening them, or let a professional do it. If the reset keeps tripping, there is an underlying fault.
Gas water heaters
On gas models, A. O. Smith points to a gas supply or pilot problem. Check that the gas valve is on and look through the sight window for the pilot flame or the status light code. Follow the lighting instructions on the label exactly; never use force on the gas control. A thermocouple or gas valve that has failed is a job for a pro.
Not enough hot water
Rheem lists running out of hot water sooner than usual, longer recovery, and rumbling or popping noises as signs of sediment buildup and recommends flushing about once a year (every six months with hard water). On electric heaters, one failed element also cuts capacity.
When to call a professional
- You smell gas (leave first).
- The breaker or the reset trips again.
- The pilot will not stay lit or the burner will not ignite.
- The heater is about 8 to 12 years old or older and having problems.
- Water is leaking from the tank.
What it usually costs
HomeGuide (2026) lists typical tank water heater repairs at $150 to $700: heating element or thermostat about $100 to $350, thermocouple about $100 to $325, gas control valve about $150 to $550. A new tank heater runs about $600 to $1,800 installed.
Frequently asked questions
Why do I have cold water but no hot water?
The water heater itself is not heating: no power or gas, a tripped reset, a failed element or thermostat, or a pilot or ignition problem.
How long do water heaters last?
A. O. Smith puts the average life of a water heater at about 8 to 12 years.
Related problems
- Water heater leaking
- Hot water smells like rotten eggs
- Breaker keeps tripping
- Low water pressure in one faucet or shower
Sources
- A. O. Smith: When to repair or replace your water heater
- Rheem: How often to flush your water heater
- A. O. Smith: Water heater maintenance guide
- HomeGuide: Water heater repair cost (2026)
This guide is general information, not a substitute for an inspection by a licensed professional. See our disclaimer.