Water Heater Not Hot Enough

Start here: what "not hot enough" looks like

The pattern tells you a lot.

• Warm but never hot, from the first minute. Thermostat set too low, a failed upper element or thermostat on an electric tank, or a gas burner that's underfiring.
• Hot for a minute, then lukewarm. Classic electric lower element failure, or a broken dip tube letting cold water mix at the top of the tank.
• Fine in summer, weak in winter. Colder incoming water.
• Fine until two people shower. The heater is probably too small for the house. See runs out of hot water fast.

1. Check the thermostat setting

It sounds too simple, but it's the first thing a plumber looks at. A.O. Smith ships its heaters preset to 120°F and calls 120°F to 140°F the safe operating range. Somebody may have turned it down for vacation, or a kid bumped the dial.

On a gas tank, the temperature dial is on the gas control valve near the bottom. Some dials show words like "Low" or "Hot" instead of degrees, and your manual says what each mark means. Turn it up a little, wait 30 to 60 minutes, and test at a faucet.

On an electric tank, the thermostats sit behind the access panels, and two-thermostat models should have both set the same. Power off first. A flat screwdriver turns them, clockwise for hotter.

Don't crank it to make up for a failing part. If the old setting used to be plenty and now it isn't, something else changed.

2. Electric tank: an element or thermostat

An electric tank has two elements. The upper one heats the top of the tank first, then hands off to the lower one. When the lower element dies, you get a small amount of hot water from the top and then it goes lukewarm. When the upper element or upper thermostat fails, you often get no real heat at all.

A.O. Smith lists faulty elements and thermostats among the main causes on electric heaters, and says elements should be tested and replaced if needed. You test them with a multimeter, breaker off. Our no hot water from an electric water heater page walks through it, and testing a water heater element covers the meter steps.

If the red reset button keeps tripping along with weak heat, that points to a grounded element or a bad thermostat.

3. Gas tank not getting hot enough

On gas, look at the burner flame through the sight window. A weak, lazy flame can mean the burner isn't getting enough air or gas.

A.O. Smith's gas list includes blocked air screens or filters, which starve the burner and should be cleared, and a clogged burner, which should be cleaned once a year with gas and water off. A gas control valve that isn't opening fully is a job for a professional. If the pilot burns but the main burner barely runs, see pilot light is lit but no hot water.

4. A broken dip tube

The dip tube is a plastic pipe that carries incoming cold water to the bottom of the tank. If it cracks or breaks off, cold water dumps into the top of the tank, right where the hot water leaves. You get warm water that cools off fast. Rheem lists damaged dip tubes as one cause of reduced hot water.

A clue: bits of white plastic in faucet aerators or shower heads. HomeGuide puts dip tube replacement at $100 to $300 installed.

5. Sediment

Sediment on the bottom of the tank takes up space and insulates the water from the burner or lower element. Rheem names it as a cause of reduced hot water supply. If your tank also pops or rumbles, that's the giveaway. A.O. Smith suggests draining a few gallons once a year to keep it under control. Our noises page covers the flush.

Tankless water heater not getting hot enough

A tankless heater has a limit on how much it can raise the water temperature at a given flow. The Department of Energy says a typical gas tankless unit manages about a 70°F rise at 5 gallons per minute, and an electric one at 2 gallons per minute. Ask for more flow than that, or feed it colder winter water, and the outlet temperature drops.

Things to try:

• Run fewer fixtures at once. A.O. Smith says an undersized unit means limiting simultaneous use or upgrading.
• Clean the inlet water filter screen, if your model has one.
• Descale it. A.O. Smith recommends descaling once a year, especially in hard water areas.
• Check the set temperature on the controller.

Heat pump water heater not hot enough

Heat pump models heat more slowly than a standard electric tank, and the heat pump needs warm air around it to work well. If the space is cold or the unit is in an efficiency-only mode, it can fall behind during heavy use. Check the mode setting in your manual and switch to a hybrid or high-demand mode before you assume a part has failed. A clogged air filter on the unit also slows it down.

When to call a plumber, and what it costs

Call if the elements test bad and you'd rather not do electrical work, if the gas burner flame looks wrong, or if the tank is old and showing other signs like rusty water. Rheem suggests planning replacement around year ten for a standard tank.

HomeGuide's repair figures:

Expect a service call fee of $50 to $200 on top in many areas. For a tank past ten years, compare the quote with water heater cost before you approve it.