Water heaters
Water heater not heating: causes and what to check
Published by Prime Plumbing · Updated · How we write our guides
Short answer
On an electric water heater, no hot water usually means a tripped breaker, a tripped high-limit reset or a failed heating element. On a gas heater it usually means the pilot is out, the thermocouple has failed or the gas valve is faulty. Check the power or pilot first; if those are fine, a part needs replacing.
What should I check first?
- Electric: the breaker in the panel, then the red reset button behind the upper access panel (power off first)
- Gas: whether the pilot light is lit, and that the gas valve is on
- The thermostat setting; 120°F is the usual recommendation
- Whether hot water is missing everywhere or at one faucet only
What are the common causes by heater type?
| Symptom | Electric heater | Gas heater |
|---|---|---|
| No hot water at all | Tripped breaker or reset, failed upper element | Pilot out, bad thermocouple or gas valve |
| Lukewarm water | Failed upper thermostat or element | Thermostat set low, sediment over the burner |
| Hot water runs out fast | Failed lower element | Broken dip tube, sediment in the tank |
| Water too hot | Thermostat stuck on | Faulty gas control valve |
Why does the reset button keep tripping?
The high-limit switch cuts power when water gets too hot. If it trips repeatedly, a thermostat is stuck on, an element is shorted or a wire is loose. Resetting it again and again is not a fix; the faulty part has to be found.
Why won't the pilot stay lit?
The thermocouple senses the pilot flame and holds the gas valve open. When it wears out, the pilot lights but goes out as soon as you release the button. A dirty pilot tube or a draft can cause the same thing. Newer heaters use an electronic igniter and flash a code on the control when it fails.
When should I call a plumber?
Call if you smell gas (leave the house and call the gas utility first), if the breaker or reset trips again after you restore it, if there is water around the heater, or if the simple checks have not brought the hot water back.
Common questions
How long does a water heater take to heat up again?
A gas tank takes roughly 30 to 60 minutes to recover; an electric tank takes about an hour or two, depending on its size and the incoming water temperature.
Is it worth repairing a water heater that is not heating?
Usually yes if the tank is under about 8 years old and not leaking. Elements, thermostats and thermocouples are inexpensive parts compared with a new heater.
Further reading from official sources
- Water Heaters (ENERGY STAR)
This guide is general information for homeowners, not a substitute for an on-site assessment. Plumbing codes and permit rules vary by city and state.