Shower no hot water: what to check

Turn the bathroom sink to hot first. Warm water there tells you the heater is fine, which puts the shower valve, its limit stop or its cartridge under suspicion. A sink that stays cold means the fault sits further back, and the water heater repair page is the better place to continue. Sixty seconds on this comparison removes half the possibilities.

Is it the shower or the whole house?

Try the bathroom sink and one kitchen faucet. When both turn hot, blame the shower hardware. When neither does, look at the heater, its power or gas supply, or a valve that has been shut. A sink that heats only after a long wait could just be a long way from the tank, which is distance rather than damage.

Some other clues:

• Hot for a minute, then cold. The tank may be too small for the shower, or a lower element has died.
• Cold at first, warm later. Long pipe runs, or a tankless unit taking a moment to start.
• Lukewarm everywhere. Probably a thermostat dialed too low.
• Hot in one bathroom, cold in another. The cold one has a valve problem.

The heater side gets a full treatment in why the whole house goes cold, and the kitchen sink version deals with that fixture.

Could the temperature limit stop be set too cold?

Yes, and it is a very common cause. Many shower valves have an adjustable limit stop that caps how far the handle can turn toward hot, so water never gets above a safe temperature. If it was set too cautiously, or the heater setting changed afterward, the shower never feels hot. Moen and Delta both document repositioning it.

On a Moen valve, the handle should reach the full-hot position, about 9 o'clock on a standard model; if it stops short, the limit stop needs moving. Delta explains that its rotational stop works in tooth-by-tooth steps, and each step can change temperature noticeably. Both brands recommend a thermometer check, with the maximum near 120°F.

On many valves this is an easy adjustment, though it has to go back together correctly, since Delta warns that omitting the disc can lead to scalds. Not sure of your valve? Let a plumber handle it.

What if the cartridge or balancing spool has worn out?

Inside the valve, a tired cartridge or a seized pressure-balancing spool can hold the mix on the cool side or make temperatures lurch. Moen's own troubleshooting suggests a new cartridge, a flush of the valve body, and a check that the spool slides freely. Pressure that sags as you rotate toward hot is another symptom.

Hard water is part of the story locally. Anaheim's own hardness page lists about 300 ppm, and minerals can gum up small passages inside a valve over time. Replacing a cartridge usually means closing the shutoffs, removing the handle and trim, and pulling the old one with the right tool. The cartridge must match the brand and series, so a photo of the trim helps. Drips at the handle are covered separately in curing a dripping shower faucet.

Is the water heater the real problem?

If the sink and shower are both cold or weak on hot, then yes. For a storage tank, breakers that tripped, pilots that died, low thermostats and burned-out elements head the list. After a long shower, a small tank can simply run dry; recovery takes time, and sediment slows it further.

The Department of Energy recommends a setting near 120°F for most homes, and the CPSC warns that water hotter than that can scald quickly, so resist turning the heater up as a quick fix. A hotter setting is a safety trade, and a mixing valve is the way to manage it if one is needed.

What about a tankless heater that goes cold mid-shower?

Most tankless models will not ignite until flow passes roughly 0.5 gallons a minute, and a stingy showerhead or a half-open valve can slip beneath it. Mineral scale, a gas supply hiccup or a fault code may also halt heating. A quick cold slug between two nearby uses is a documented quirk.

California's Title 20 sets the showerhead ceiling at 1.8 gpm, measured at 80 psi, so flows here are modest by design, which makes sizing with some margin worthwhile. Our pages on tankless heaters with no hot water and water coming out cold from the faucet go through the checks for those cases.

At what point is this a job for a plumber?

Book a visit if the sink is cold as well, when a breaker keeps tripping, when the valve hides behind finished wall with no access, or when a new cartridge changes nothing. Gas piping and heater work sit in the state's C-36 plumbing class, and a replacement heater needs a city permit.

A gas smell overrides everything: get outside, then phone SoCalGas via 1-800-427-2200, or 911 if a person is hurt. For ordinary jobs, use our quote form. It helps to say which fixtures are affected, what you have already checked and whether the heater is gas, electric or tankless.