Start with what kind of heater you have, because the likely cause changes with it. Gas tank: the pilot or burner failed. Electric tank: a tripped breaker, a reset button or a dead element. Tankless: an error code, an interrupted gas or power feed, or scale buildup. Hot water that is merely weak, or that runs out fast, is a different symptom, covered on our water heater repair hub.
Which kind of water heater do I have?
Read the label, then look at the base. A gas tank has a burner compartment near the floor, a vent on top and a gas line with a shutoff. An electric tank has thick wires going in at the top or a side access panel and no vent. A tankless unit is a wall-mounted box about the size of a suitcase.
Most Mission Viejo homes built in the planned-community years have a tank in the garage or a closet. Some have a tankless unit that was added later. The label also gives the model, the serial number and the tank size, which you should photograph before you call anyone. If the heater serves more than one unit, such as a condo with a shared system, the fault may sit beyond your own front door. The renter section further down covers that case.
Which quick checks come before calling anyone?
Work through five small tests in order: are all taps cold, is power or gas reaching the heater, and has a pilot or reset button dropped out. Ten minutes covers all of them and clears more cold-water calls than you would expect. Never open a gas line yourself, and go outside at any hint of gas.
- Open the hot tap farthest from the heater and let it run two minutes. When one fixture alone stays cold, suspect its mixing valve or cartridge instead of the heater.
- Look at the electric panel. A tripped double breaker means the heater stopped drawing power.
- Look through the viewing window of a gas heater. No pilot flame means relighting is the next step, which the pilot light repair page covers.
- Try the red reset button on an electric tank, found behind the upper access panel. Open the panel only with the breaker off.
- Check the dial. A thermostat left on vacation or bumped to low gives lukewarm water that feels like a failure.
A dial setting is only a hint. Wikipedia points out tank thermostats are a poor guide to the real temperature inside, so a high setting can still deliver cool water after an element dies.
What stops a gas heater from making hot water?
Four causes dominate: a pilot that went out, a sensor that no longer proves the flame, an interrupted gas supply, or a burner choked with dust. Smell gas and you stop and walk out, then tell the gas utility from outdoors.
A flame that keeps dying suggests a worn sensor or a draft near the vent. Relighting is routine and the steps are printed on the label. Quit after a second failed attempt. Gas appliances and gas lines are regulated, and swapping parts beside the burner belongs with a plumber. The pilot light repair article goes through what a plumber checks.
What goes wrong with an electric heater?
An electric tank carries a pair of elements, upper and lower, each with a thermostat of its own. When the upper element or thermostat dies, almost nothing comes out hot. When the lower one dies, the supply merely shrinks. A tripped breaker or high-limit button is the cheaper explanation.
Check the breaker first and the reset button next, keeping the power off while the panel is open. A breaker that flips straight back is a stop sign, because a shorted element or damaged wiring is a safety matter. Our no hot water, electric heater article goes through element and thermostat testing, and which steps need an electrician or plumber.
Could it be a tankless water heater, or something else?
Yes. A tankless unit flashes an error code when it fails to ignite, loses airflow or senses a fault. Match the code to the manual, confirm gas and power, and look at the vent. Repeat faults often trace to scale from hard water, and descaling may be the cure. See the gas tankless repair page.
Other causes sit outside the heater. A failed mixing valve in a shower gives cold water with a healthy heater. A cross-connection somewhere in the plumbing can feed cold water into the hot side. A washing machine that fills cold only points at its own valve or the supply line, and the washing machine no hot water page covers that. If heating works but the water is cold, the no hot water but heating works page covers why those two systems are separate.
Does a cold shower mean I should phone tonight?
Rarely. A day of cold showers is a nuisance. It turns urgent with water around the heater, a gas smell, a vulnerable person at home, or taps that swing between scalding and icy. Per Wikipedia, skin can burn in under 5 seconds at 140 degrees Fahrenheit, so give an overheating tank room.
With water pooling, close the cold valve on top and stop the power or gas. The emergency heater repair page covers jobs that cannot wait for a regular slot. A cold heater with no leak can generally hold until a daytime visit, which costs less than an after-hours one.
What if I rent an apartment and have no hot water?
California Civil Code 1941.1 expects a rental's supply to deliver hot as well as cold water, and a home that cannot may count as untenantable. Tell the landlord in writing, keep a copy and date your photos. The apartment no hot water laws guide covers the next steps.
Leave the landlord's equipment alone. A tenant who dismantles an owner's heater can end up in a dispute over damage. A plumber we arrange can visit once the landlord agrees. For a shared system, start with the building manager.
Who fixes what when the water runs cold?
A plumber handles failed elements, thermostats, pilot assemblies, valves and tanks. SoCalGas takes the gas smell. A renter rings the landlord, and an electrician handles a breaker that trips right after resetting. Expect a written quote before any heater replacement starts.
To book, send the heater type, model number and your checks through the quote request. Other jobs we arrange are listed on the home page.
Common questions
Why does the hot supply run dry so quickly?
Look first at the lower element of an electric tank, sediment on the tank floor, or a cracked dip tube. Any of them leaves less usable hot water in the tank. A thermostat turned down does the same. Gas tanks heavy with sediment also rumble or pop while they heat.
Why does a shower start hot and then turn cold?
Common reasons: an upper element or thermostat on its way out, or a tank undersized for the household. Tankless units can do it when flow is below their minimum or when scale limits the heat exchanger. A plumber can test the element and thermostat and tell you whether it is worth repairing.
Does a Rheem heater with no hot water have a standard fix?
No. A Rheem tank fails the same way any tank does: pilot, sensor, element, thermostat or sediment. The model label tells the plumber what to bring. Check whether the heater is under a manufacturer warranty by finding the serial number and the receipt before anyone takes it apart.
Could a boiler be the reason?
If your home heats water through a boiler, yes. A boiler can lock out, run low on pressure or lose power, and the hot tap goes cold at the same time. Check the boiler's display for a fault code, and read the manual before touching controls. A plumber or heating contractor handles the repair.
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