Start with the scope. Is the hot water cold at every fixture, or only at one? A single cold shower or sink points to a mixing valve or faucet cartridge rather than the heater. Cold water everywhere points back to the heater, its fuel supply or its controls.
Next, identify the heater. The rating plate tells you whether it's gas or electric, tank or tankless. The checks below are different for each type, and so are the likely causes.
Safe checks before you call
Stop at any point if you smell gas, see water on the floor or are unsure what you're looking at.
- Gas tank: look through the sight window on the burner compartment for the pilot or burner flame.
- Gas tank: check that the gas control knob is set to On, not Pilot or Off.
- Gas, any type: check whether other gas appliances, such as the range, are working.
- Electric tank: check the breaker panel for a tripped double-pole breaker labeled for the water heater.
- Tankless: read the error code on the display and look it up in the owner's manual.
- Tankless: confirm the unit has power, since even gas tankless models need electricity.
- Any type: note whether the water is cold, lukewarm or runs out quickly. Those symptoms point to different causes.
Common causes by heater type
| Heater type | Frequent causes of no hot water | Who handles it |
|---|---|---|
| Gas tank | Pilot out, failed thermocouple or flame sensor, faulty gas control, venting safety shutoff | Relight per label if no gas smell; otherwise a plumber |
| Electric tank | Tripped breaker, high-limit cutoff tripped, failed element or thermostat | Breaker reset by owner; electrical diagnosis by a pro |
| Gas tankless | Ignition fault, scale, clogged inlet screen, gas supply or venting error | Plumber, using the error code as a starting point |
| Any | Tank failure combined with a leak | Replacement assessment |
Example: cold showers after a windy night
Illustrative example. Not a real job or customer.
A homeowner in an older Orange tract home wakes up to cold water. The gas heater in the garage shows no flame in the sight window, and there's no gas smell.
- They follow the lighting instructions on the heater's label to relight the pilot.
- The pilot lights but goes out again when the knob is released after the stated hold time.
- They turn the control to Off and stop trying.
- A plumber finds a worn thermocouple and checks the venting and the gas control while there.
A part repair, with no replacement needed. Repeated relighting would not have fixed it.
Questions to ask when you call
- Based on the symptoms and the error code, what do you suspect?
- Will you check the venting and gas connections as part of the visit?
- How will the repair be priced, and will I get it in writing first?
- If replacement comes up, what makes you say the tank isn't worth repairing?
Common questions
Why do I have hot water but it runs out fast?
On a tank heater, sediment from hard water, a failed lower element on an electric unit, or a broken dip tube can all shorten the hot water supply. The heater may also be too small for the household.
My electric heater's breaker keeps tripping. Can I keep resetting it?
No. A breaker that trips repeatedly points to an electrical fault such as a shorted element or damaged wiring. Leave it off and have it diagnosed.
Does a gas tankless heater work during a power outage?
Most don't, because their controls, ignition and fan need electricity. Check your model's manual.
General information for Orange, not a quote or professional advice. In an emergency, call 911.