Water heater not hot enough: how to find the cause

1. One fixture or the whole house?

Run hot water at the kitchen sink and measure it with a kitchen thermometer. If the sink is hot but the shower isn't, the water heater is fine. If everything is lukewarm, it's the heater or its supply. Our guide to hot water at the sink but not the shower goes deeper on the single-fixture case.

2. The shower valve limit stop

Most single-handle shower valves have a limit stop that caps how far the handle turns toward hot, as scald protection. Delta's instructions: let the water run until it's fully mixed, turn the handle to the hottest position and measure with a thermometer in a plastic cup. On its Monitor 1300 and 1400 series, each tooth of the stop changes the maximum by about 6°F. Moen says that with the handle fully rotated and the stop at full hot, the shower will match the temperature set on the tank. Both recommend keeping shower water at or below 120°F, and Delta notes local plumbing codes may cap it at 110°F or 120°F.

3. The thermostat setting

A. O. Smith's Bulletin 36 notes heaters are now factory preset at a lower temperature than in the past. Its test procedure sets the dial so the water comes out between 120°F and 140°F. Raising it gives more usable hot water but raises the scald risk. Meridian, Idaho's home safety guide asks whether your heater is set to 120°F or less for that reason (see our Meridian page). Our guide to water heater temperature covers the trade-off.

4. A failed element or thermostat (electric)

A. O. Smith lists faulty heating elements and thermostat problems among the most common causes of water that won't get hot. It says thermostat problems can trip the red high-limit reset button, often because of a grounded element or a faulty lower thermostat. Turn the breaker off before opening any panel. Our guide to a bad electric water heater element walks through testing.

5. Gas supply or burner (gas)

On gas heaters, A. O. Smith points to gas supply problems that stop the burner lighting or put the pilot out, and blocked combustion air screens or filters that hurt burner performance. Make sure the gas valve is open; beyond that, A. O. Smith says gas supply problems may need professional help. If the pilot keeps going out, see pilot light keeps going out.

6. Sediment and scale

A. O. Smith says mineral buildup clogs and damages heating elements, and recommends descaling yearly in hard water areas. See how to flush a water heater. Age matters too: the median home in Mead, Colorado was built in 2006, so many original heaters there are about 20 years old (see our Mead page). Check how old yours is before paying for repairs.

7. A broken dip tube, or not enough heater

A. O. Smith's not-enough-hot-water test (Bulletin 35 for gas, 36 for electric) separates these. After a 15-gallon draw, a gas heater should recover in about 20 to 35 minutes, and an electric heater in about 45. Run hot water until 60% of the tank is used. The temperature should fall about 30°F. If it drops much more, check the dip tube (and on electric, the lower element). See our dip tube guide.

If it passes, the heater may simply be too small for how you use it. A. O. Smith suggests limiting simultaneous hot water use or upgrading to a higher-capacity model, and notes gas tanks need about 30 to 40 minutes to recover and electric tanks 60 to 90. See what size water heater you need.

Local pages mentioned

• Mead, CO
• Meridian, ID