No Hot Water? What It Means and What to Check First

No hot water anywhere in a San Jose home almost always means the water heater has stopped heating: the pilot or burner is out on a gas heater, a breaker or the high-limit switch has tripped on an electric one, or a tankless or heat pump unit has shut down with an error code.

Hot water that runs out fast or is only lukewarm points to a different set of causes, such as sediment, a failed element, a low thermostat setting or a heater too small for the household. This guide for San Jose and South Bay homeowners explains what each symptom means, the checks you can safely do yourself, and when to call a licensed plumber.

Safety first. If you smell gas (a rotten-egg or sulfur smell) near the water heater, don't relight anything or touch switches: leave the house and call 911 and PG&E at 1-800-743-5000 from outside. On an electric heater, turn the power off at the breaker before opening any access panel: the wiring behind it carries 240 volts. Never cap, plug or remove the temperature and pressure (T&P) relief valve or its discharge pipe, and never bypass a safety switch that keeps shutting the heater off. Those devices are what keep a tank from overheating or bursting.

What Does “No Hot Water” Usually Mean?

Start with two questions: is the whole house without hot water, or only one fixture? And is there no hot water at all, or just not enough? The table matches the common symptoms to their usual causes.

Checked October 2026 against the manufacturer sources listed at the end.

Is It the Whole House or One Fixture?

Run hot water at the kitchen sink, a bathroom sink and a tub. If every fixture is cold, the problem is at the water heater. If one shower or faucet runs cold while the others are hot, the heater is working: the fixture’s cartridge or its pressure-balancing (anti-scald) valve has failed or is set too low. That’s a plumbing repair on the fixture, not a water heater job.

Gas Water Heater With No Hot Water

Gas tank heaters are still the most common kind in San Jose homes, and most no-hot-water calls on them come down to the pilot, the gas supply or a safety shutdown.

Is the Pilot or Burner Lit?

Many gas heaters have a small sight window near the bottom. With a standing pilot, you should see a small steady flame. If it’s out and you don’t smell gas, you can relight it by following the lighting instructions on the heater’s label exactly; our gas water heater page describes the usual sequence. Newer heaters with electronic ignition have no manual pilot; their status light blinks a code that the manual explains.

A pilot that goes out again within hours or days usually means a worn thermocouple or flame sensor, a failing gas control valve, or a draft or venting problem. Those are repairs for a plumber, and a venting problem should be checked promptly because combustion gases need to leave the house.

Is the Gas Supply On?

Check that the shutoff valve on the gas line to the heater is open (the handle runs in line with the pipe). If the stove and furnace also have no gas, the supply to the house is off; call PG&E. Don’t turn on a gas meter valve yourself.

Did a Safety Switch Shut the Heater Down?

Modern gas tank heaters have safety devices that shut off the burner and pilot if they sense overheating, a lack of combustion air or flammable vapors near the heater. A.O. Smith lists blocked air screens among the causes of a gas heater that stops heating. Keep the area around the heater clear of boxes, laundry lint, paint and solvents. If a safety switch has tripped, a plumber needs to find out why before the heater goes back into service; resetting it without fixing the cause just lets it trip again, or worse.

Electric Water Heater With No Hot Water

Check the Breaker

A.O. Smith calls a tripped breaker the most common reason an electric heater stops heating. Find the double breaker for the water heater in your panel and reset it once. If it trips again, leave it off: something is shorted, often an element, and it needs a plumber or electrician.

The High-Limit (Reset) Button

Electric tanks have a high-limit switch with a red reset button behind the upper access panel. It trips when the water gets too hot. A.O. Smith says to turn off the power at the breaker before touching anything, then press the button until it clicks. Only do this if you’re comfortable removing the panel with the power off; insulation and live terminals sit right behind it.

A high-limit switch doesn’t trip without a reason. The usual causes are a thermostat that has stuck on or a shorted element. If it trips a second time, the heater needs a repair, and resetting it again isn’t the fix.

Lukewarm Water From an Electric Heater

Most electric tanks have two elements. When the lower one fails, the heater still makes some hot water but runs out quickly; when the upper one or its thermostat fails, there may be none at all. Testing elements and thermostats means working on 240-volt circuits, so leave it to a plumber. Element and thermostat replacements are routine repairs on a heater that’s otherwise in good shape.

Tankless Water Heater: No Hot Water or Cold Bursts

A tankless heater only fires when enough water flows through it. Rinnai, for example, says its units need 0.4 to 0.6 gallons per minute through the hot side to ignite and shut off when the flow drops below about 0.26. A trickle from one faucet, a clogged aerator or a dirty inlet filter can keep the flow below that, so the water never gets hot or turns cold partway through.

• Open the tap fully and see whether the heater fires.
• Clean the aerators on the faucets you use most.
• Read the display. An error code points to the cause; the manual lists what each one means and which ones you can clear.
• Check the inlet filter on the cold-water connection if your manual shows you how.

A brief burst of cold water between two uses, sometimes called a cold-water sandwich, is normal for many tankless units. A.O. Smith recommends descaling tankless heaters every year, especially where water is hard. Scale, ignition problems, gas pressure and venting are jobs for a plumber; see tankless water heater repair.

Heat Pump Water Heater: Slow or No Hot Water

A heat pump water heater pulls heat from the air around it. ENERGY STAR says it should sit in a space that stays between 40°F and 90°F year-round with about 1,000 cubic feet of air around it, may need its air filter changed yearly, and switches to a backup electric mode in colder conditions. So first:

• Read the display for an error code or alert.
• Check the air filter, following the manual.
• Check the mode. In heat pump-only (efficiency) mode it recovers more slowly than in a hybrid or high-demand mode.
• Check the space. A closet with the door closed or a cold garage can starve it of warm air.

If it shows a repeating code or never leaves backup mode, have it serviced. See heat pump water heaters and what a heat pump water heater costs in San Jose.

Hot Water Runs Out Fast or Is Only Lukewarm

When there’s some hot water, but not enough, the heater is working at less than full capacity:

• Temperature setting. The Department of Energy suggests 120°F for most homes. A dial that’s been bumped lower gives you less usable hot water.
• Sediment. Minerals settle at the bottom of a tank, take up space and insulate the water from the burner. Popping or rumbling while it heats is the usual sign. A.O. Smith recommends flushing the tank regularly; our water heater maintenance tips explain how.
• A failed element or thermostat on an electric heater (above).
• A broken dip tube. The tube carries incoming cold water to the bottom of the tank. If it breaks, cold water mixes in at the top and the hot water runs out fast.
• The heater is too small. A new bathroom, a bigger tub or more people in the house can outgrow a heater that used to be enough. Incoming water is colder in winter, so a marginal heater runs out sooner then.
• Recovery time. After a heater runs out, A.O. Smith gives about 30 to 40 minutes for a gas tank to recover and 60 to 90 minutes for an electric tank.

If the hot water also smells like rotten eggs, the cause is usually inside the tank: Bradford White explains that the odor needs sulfur, hydrogen and bacteria, and the anode rod supplies the hydrogen. A plumber can replace the anode with a different type and disinfect the tank. Don’t simply remove the anode: Bradford White notes that voids the warranty and shortens the tank’s life. If the smell comes from drains rather than the water, see sewer smell in the house.

What Can You Safely Check Yourself?

Safe to do:

• Test several fixtures to see whether it’s the heater or one fixture.
• Look at the pilot through the sight window, and relight a standing pilot by the label’s instructions if there’s no gas smell.
• Check that the gas valve to the heater is open.
• Reset the water heater’s breaker once.
• Check the thermostat setting and the display code.
• Clean faucet aerators, and the heat pump filter or tankless inlet filter as the manual shows.
• Keep the area around the heater clear.

Leave to a licensed plumber:

• Anything to do with gas piping, the gas control valve, the burner or the venting.
• Resetting a tripped safety switch on a gas heater, or a high-limit switch that has tripped more than once.
• Testing elements or thermostats on a live electric heater.
• Anything to do with the T&P relief valve beyond the yearly test the manual describes (see what to do when a water heater is leaking).

Should You Repair or Replace the Water Heater?

Most no-hot-water problems are repairs: a thermocouple, a gas valve, an element, a thermostat, an igniter or a control board. Replacement makes sense when the tank itself is leaking, which can’t be repaired, or when the heater is over about 10 years old and needs a costly part. Our guides to the signs a water heater needs repair or replacement and the common causes of water heater failure go further.

CPI Service prices, October 2026. Replacement prices include the City permit. See water heater installation cost for what moves the price.

No Hot Water in San Jose: What’s Different Here

• Permits. Replacing a water heater in San Jose takes a permit and an inspection, with earthquake straps, proper relief valve piping and, where required, an expansion tank. We pull the permit and schedule the inspection.
• The Air District rule. The Bay Area Air District has adopted a rule that requires new small tank water heaters to be zero-NOx. It doesn’t affect a working heater, but it shapes what you can buy when yours fails. See Bay Area zero-NOx rules.
• Hard water. Moderately hard South Bay water leaves sediment in tanks and scale in tankless heat exchangers, so flushing and descaling matter here.
• Rebates. Switching from gas to a heat pump water heater can qualify for local rebates; see rebates by city before you replace in a hurry.

When Should You Call a Licensed Plumber?

Call when:

• you smell gas (call 911 and PG&E from outside first)
• the pilot won’t light or won’t stay lit
• a breaker, high-limit switch or gas safety switch trips again after one reset
• the heater shows an error code that comes back
• water is leaking from the tank or the relief valve
• you see soot, scorching or melted parts near the burner or the top of the heater
• the heater is over 10 years old and the hot water keeps getting worse

CPI Service repairs and replaces gas, electric, tankless and heat pump water heaters throughout San Jose and the South Bay, with same-day service and a 24/7 emergency line. We’re licensed under CSLB License #1101278 (C-36 Plumbing), every job is quoted as a fixed price before we start, and our work carries a 1-year labor warranty. If you’re replacing the heater, we offer $250 off water heater installation and 0% interest financing for 12 months, subject to approval. See water heater services, request a free estimate or call (408) 978-3093.

Sources

• A.O. Smith: Is Your Hot Water Not Getting Hot? Common Causes and What to Do
• Rinnai: FAQ (minimum flow)
• U.S. Department of Energy (FEMP): Purchasing Energy-Efficient Residential Water Heaters
• ENERGY STAR: Heat Pump Water Heaters
• Bradford White: Hydrogen Sulfide Odor / Rotten Egg Smell and Chlorinating Water Heaters
• PG&E: Gas Safety

Checked October 2026.