No Hot Water: Causes and Fixes for Gas, Electric, and Tankless Water Heaters

The most common causes of no hot water are also the simplest: a tripped breaker, a pilot that went out, a gas control left on vacation, or a tankless unit that is not seeing enough flow. A failed element, thermostat, or gas control, or a leaking tank, belongs to a plumber or technician.

Below: how to narrow it down, the causes for gas, electric, and tankless heaters in the order to check them, and hot water that runs out fast or stays lukewarm. For a heater that pops or rumbles, see water heater popping noise.

Start Here: Narrow It Down

One faucet or the whole house? Try the hot water at a sink on another floor. If only one faucet or shower is cold, the heater is fine: the problem is that fixture's worn or stuck cartridge or mixing valve, or a single-handle faucet's limit stop set too far toward cold. That is a faucet repair, not a heater repair.

None at all, or not enough? Cold everywhere means the heater is not heating; find your type below. Hot water that runs out fast or stays lukewarm is its own list, further down.

Which type? A gas tank has a gas line, a control knob, and a vent pipe. An electric tank has a heavy cable and screw-on side panels. A tankless heater is a box on the wall.

Most Likely Causes

Gas tank water heaters

1. The pilot is out, or the burner will not light. Check the flame window or status light near the bottom. Relight only if you do not smell gas, and only by following the lighting instructions on the heater's label, exactly; A.O. Smith says the heater's own instructions come first. They begin with the control off and a wait so gas can clear (at least 10 minutes in A.O. Smith's guide). If the pilot will not light, or goes out when you release the knob, stop: the thermocouple or flame sensor and the gas control are the technician's, and propane safety guidance says never to troubleshoot a pilot that keeps going out.
2. The gas supply or the control setting. If no gas appliance works, call the gas utility. After a propane run-out, the retailer or a qualified technician must leak-check the system, restore service, and light the pilots. The heater's gas shutoff is open when its handle lines up with the pipe; if it is closed and you do not know why, call. The knob may still be on Vacation or Low, or on Pilot, which does not heat. Power-vent models also need to be plugged in.
3. A flammable vapor lockout. Some newer gas tank heaters, including some Rheem models, have a flammable vapor sensor near the base. Rheem's service literature says that when it detects gasoline or similar vapors, the control shuts down, stays locked out until reset, and flashes a code. If you smell gasoline or solvent strongly, treat it like a gas smell: leave, don't switch anything on or off, and call from outside. Otherwise, air out the space and remove the gasoline, paint, or solvent. Some models need a technician to reset the lockout and check the sensor. Follow your manual, and if it locks out again, call the technician.
4. Blocked venting or combustion air. A.O. Smith lists blocked air screens among the causes of poor burner performance and warns that too little air can put carbon monoxide into the house. Keep boxes and lint away from the base. Soot means a technician visit before you use the heater again. Working CO alarms on every level are the backstop; if one sounds, get everyone outside and call 911.

Electric tank water heaters

1. A tripped breaker. A.O. Smith calls it the most common cause. Many electric heaters run on 240 volts through a double breaker, and some have two breakers. Switch a tripped one fully off, then on, and check any disconnect switch at the heater. If it trips again, leave it off; our breaker keeps tripping page explains why.
2. The high-limit (ECO) reset button. It cuts power to the elements if the water overheats and stays off until its red button, behind the upper access panel, is pressed. Manufacturers differ, so follow your manual. A.O. Smith's homeowner steps: power off at the breaker (confirm it's dead with a non-contact voltage tester), remove the upper panel, press the button until it clicks, replace the insulation and panel, restore power. Rheem's and Bradford White's manuals are stricter: an overheat means something failed, and a qualified technician should find the cause first. If it trips again, leave the breaker off and call.
3. A failed element or thermostat. Most electric tanks have an upper and a lower element, each with a thermostat. A failed upper element usually means no hot water at all. Testing means working on 240-volt parts with a multimeter, and Rheem and Bradford White both tell owners not to attempt repairs to elements, thermostats, or wiring. That is a pro's job.

Tankless water heaters

1. An error code on the display. Write it down before resetting anything, and look it up in the manual. Codes vary by model, and Rinnai and Navien both send owners to the installer or their technical support for anything past a simple reset.
2. Gas or power supply. A gas tankless unit needs electricity too; Rinnai notes it will not run without power. Check that it is plugged in and its breaker is on, and whether other gas appliances work.
3. Flow below the activation rate. Rinnai's units need about 0.4 to 0.6 gallons per minute to ignite and 0.26 to keep running; other brands list theirs in the manual. Rinnai's fixes: lower the temperature setting a couple of degrees so the faucet draws more hot water, clean faucet aerators, and have the unit's inlet filter cleaned.
4. Scale buildup. Minerals coat the inside over time, faster with hard water. Rinnai calls for flushing at least once a year, done by a professional; follow your manufacturer's descaling procedure, not a tank-style flush.
5. Venting in cold weather. Rinnai warns that snow or ice can block the vent terminal or condensate drain, and Navien notes a frozen drain can trigger a blockage code. Clear snow from the outside terminal; anything frozen inside is a technician call. Freeze protection needs power, so both makers say to drain the unit in a long outage during a freeze. For the pipes, see our frozen pipes guide.

Hot water that runs out fast or is lukewarm

1. The thermostat is set too low. On many gas controls, Hot is about 120°F. Check with a kitchen thermometer under the tap first thing in the morning, as the CPSC suggests. An electric tank's two thermostats sit behind the panels; with the breaker off, both should match.
2. Sediment. Minerals on the tank bottom take up space and insulate the water from the burner or element, so recovery slows, Bradford White explains. The fix is a yearly flush; see our flush guide.
3. A broken dip tube. It carries incoming cold water to the tank bottom; cracked, it lets cold mix into the hot at the top. In A.O. Smith's check, water drawn after about 60 percent of the tank should be only about 30°F cooler; a bigger drop points to the dip tube, which a plumber replaces.
4. A failed lower element (electric). The lower element does most of the reheating, A.O. Smith notes, so when it fails you get a short run of hot water, then cold.
5. A tank too small for the household. A heater that suited two people may not keep up with four or a soaking tub, Bradford White says. Stagger showers and laundry, and size up at replacement. Colder winter inlet water also takes longer to heat, which Rheem calls normal.

On tankless, two showers at once can exceed capacity, and a brief cold burst between hot draws is what A.O. Smith calls the cold water sandwich.

When the Tank Itself Is Failing

Never cap or plug the T&P relief valve. The temperature-and-pressure relief valve on the tank protects it from overheating and overpressure; Rheem and Bradford White both say never to plug its outlet or discharge pipe. If it drips or discharges, often from thermal expansion, Rheem says that must be corrected: call a plumber.

Water at the base or rust on the tank means replacement is coming. Water from a fitting, the drain valve, or the relief valve pipe can often be fixed, but when the tank itself leaks, A.O. Smith says the heater usually needs replacing. Close the cold supply valve on top, turn off the gas control or the breaker, and call a plumber. Our leak alarm guide covers the pan and alarm that catch a slow leak before a flood.

What You Can Fix Yourself

• Relight a pilot exactly per the label, if you do not smell gas.
• Turn the gas control from Vacation, Low, or Pilot back to normal.
• Reset a tripped breaker once, and the ECO once with the power off if your manual allows it.
• Clear snow from vent terminals, clean aerators, and set the thermostat to 120°F (on an electric tank, only with the breaker off).

When to Call a Pro

Call a plumber or gas technician when a pilot will not stay lit, a lockout returns, a breaker or the ECO trips twice, a part or the T&P valve is suspect, a tankless code will not clear, or water appears at the base of the tank. Note the model, serial number, and any status code for the visit.

Prevent It

Flush the tank yearly, more often with hard water, and descale a tankless unit on its maker's schedule. Have a plumber check the anode rod; A.O. Smith suggests yearly, since a spent anode leaves the tank to corrode. Keep the heater at 120°F, keep solvents and gasoline away from it, put a leak alarm at its base, and check outdoor vent terminals before winter.

Frequently Asked Questions

How long until I have hot water after a relight or reset?

A.O. Smith puts full recovery at about 30 to 40 minutes for a gas tank and 60 to 90 minutes for electric. A tankless unit has no tank to reheat.

I just flushed the tank and now there is no hot water. Why?

On an electric heater, the power probably came back on before the tank was full; an element running without water burns out, and A.O. Smith notes the upper element then needs replacing. On a gas heater, the pilot may have gone out, or the control is still on Pilot or Vacation.

We were away for two weeks and the water is cold. What now?

Check that the gas control is back from Vacation to its normal setting, or that the breaker is on. Rheem also cautions that a system unused for two weeks or more can collect extremely flammable hydrogen gas: before using any electrical appliance connected to the hot water, run the kitchen hot tap for several minutes, with no smoking or open flame nearby.

The Bottom Line

One cold faucet is a fixture problem. Otherwise, check the easy things for your type: pilot, gas, and control setting; breaker and, if your manual allows, one ECO reset; code, power, and flow on tankless. Call when a reset will not hold, and leave first if you smell gas. Keep it at 120°F, never plug the relief valve, and treat a leaking tank as the start of a replacement.

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