If your water isn’t hot enough, first check the thermostat setting—it may have been bumped lower. If the setting is correct, the problem is likely sediment buildup (flush the tank), a broken dip tube, or a failing heating element. Gas heaters may have pilot light or thermocouple issues.
When your hot water isn’t as hot as it should be, or runs out faster than it used to, something has changed in your water heater. Most causes are fixable with DIY troubleshooting.
Quick Diagnostic Checklist
Run through these checks first:
- Has anyone adjusted the thermostat? Check the temperature setting
- Is demand exceeding capacity? Multiple showers back-to-back?
- Is it all hot water or just some locations? Whole-house vs single fixture
- Did it happen suddenly or gradually? Sudden suggests failure; gradual suggests sediment
- How old is the water heater? Units over 10-12 years may be failing
Adjusting the Temperature Setting
Start with the simplest possibility—the thermostat.
Gas Water Heater Temperature Adjustment
- Locate the temperature dial on the gas control valve (lower front of tank)
- Most have settings like “Warm,” “Hot,” and “Very Hot” plus a degree scale
- Turn the dial to your desired setting
- Wait 2-3 hours for the tank to reach the new temperature
- Test at a faucet with a thermometer
Electric Water Heater Temperature Adjustment
- Turn off power at the circuit breaker (typically 30A double-pole)
- Remove the access panel(s) on the tank (upper and lower)
- Pull back the insulation to expose the thermostat
- Use a flathead screwdriver to adjust the temperature dial
- Both thermostats (if two) should be set to the same temperature
- Replace insulation and panels
- Restore power
- Wait 2-3 hours and test
Use a cooking thermometer at a faucet to measure actual water temperature. Let the hot water run for 2 minutes first to flush the pipes, then fill a cup and measure. The setting on the heater doesn’t always match actual output temperature.
Recommended Temperature Settings
- 120°F: Standard recommendation—reduces scalding risk and energy use
- 140°F: Better for dishwashers without booster heaters, households with immunocompromised members
- Higher than 140°F: Scalding hazard, accelerates tank wear—not recommended
Sediment Buildup: The Hidden Problem
Minerals in water settle at the bottom of the tank over time. This sediment:
- Reduces effective tank capacity
- Insulates the burner from the water (gas heaters)
- Causes uneven heating
- Makes noise (popping, rumbling)
- Accelerates tank corrosion
Signs of Sediment Buildup
- Water not as hot as it used to be
- Hot water runs out faster than before
- Popping or rumbling noises when heating
- Rusty or discolored hot water
- Takes longer to reheat after use
How to Flush Your Water Heater
Do this annually to prevent buildup:
Gas heater flush:
- Turn the gas control to “Pilot”
- Connect a garden hose to the drain valve at the tank bottom
- Run the hose outside or to a floor drain
- Open a hot water faucet somewhere in the house (allows air in)
- Open the drain valve
- Let water flow until it runs clear (may take several gallons)
- Close the drain valve
- Close the hot water faucet once tank refills and flows steadily
- Return gas control to normal setting
Electric heater flush:
- Turn off power at the breaker
- Follow the same steps as gas heaters
- Restore power only after tank is completely full
The first water out will be scalding hot—be careful. If sediment has built up significantly, you may see chunks or sandy material in the water. Keep flushing until the water runs clear.
Severe Sediment Problems
If flushing doesn’t improve performance:
- Sediment may be hardite (calcite deposits)
- May need professional descaling
- Tank may be too far gone—replacement might be more economical
Dip Tube Problems
The dip tube directs cold incoming water to the bottom of the tank, where it’s heated. If it breaks, cold water mixes with hot at the top.
Signs of a Broken Dip Tube
- Hot water runs out very quickly
- Water is lukewarm but never truly hot
- Small plastic pieces appearing in faucet aerators or fixtures
- Problem appeared suddenly (tube broke)
Dip Tube Background
In the 1990s, many water heaters were installed with defective dip tubes that deteriorated rapidly. If your heater is from this era, dip tube failure is common.
Checking and Replacing the Dip Tube
This is a moderate DIY task:
- Turn off power/gas and water supply
- Drain the tank partially (enough to work without flooding)
- Locate the cold water inlet on top of the tank
- Disconnect the cold water line
- Remove the dip tube fitting (may need a large socket or pipe wrench)
- Pull out the old dip tube (or what’s left of it)
- Install the new dip tube with Teflon tape on threads
- Reconnect the cold water line
- Refill the tank before restoring power/gas
If pieces of the old dip tube have clogged fixtures, clean aerators and showerheads.
Heating Element Issues (Electric Heaters)
Electric water heaters have upper and lower heating elements. Either can fail.
Symptoms by Element
Upper element failure: No hot water at all (upper element heats first)
Lower element failure: Some hot water initially, then runs out fast (lower element maintains temperature)
Testing Heating Elements
Requires a multimeter:
- Turn off power at the breaker
- Remove access panels
- Pull back insulation
- Identify the element terminals
- Disconnect wires from one element
- Set multimeter to ohms (Ω)
- Touch probes to the element terminals
- Reading should be 10-30 ohms (check element rating)
- No reading or infinite means element is bad
- Repeat for the other element
Replacing a Heating Element
- Turn off power
- Drain tank (completely if replacing lower element)
- Disconnect wires from faulty element
- Remove element with element wrench (specialized tool)
- Install new element with new gasket
- Reconnect wires
- Refill tank completely before restoring power (elements burn out instantly if dry)
Gas Water Heater Specific Issues
Pilot Light Problems
If the pilot is out, the water won’t heat at all.
Relighting the pilot:
- Turn gas control to “Pilot”
- Press and hold the pilot button
- Use the built-in igniter or a long lighter to light the pilot
- Hold the pilot button for 30-60 seconds
- Release and verify pilot stays lit
- Turn control to desired temperature
If the pilot won’t stay lit, the thermocouple may be failing.
Thermocouple Issues
The thermocouple senses the pilot flame and allows gas flow. If it fails:
- Pilot lights but won’t stay lit when you release the button
- No gas flows to the main burner
Thermocouple replacement is a moderate DIY task—the part costs $10-20.
Burner Problems
If the pilot is lit but the main burner won’t ignite:
- Thermostat issue
- Gas valve failure
- Burner orifice clog
Burner and gas valve problems typically require a professional.
When Hot Water Is Only Lukewarm
If water never gets truly hot:
- Thermostat set too low
- Heating element failing (electric)
- Burner not firing fully (gas)
- Dip tube broken
- Crossover in plumbing (hot and cold mixing somewhere)
Checking for Plumbing Crossover
A single-handle faucet or mixing valve can allow cold water to mix with hot if the cartridge fails:
- Turn off the cold water supply to the house
- Open a hot water faucet
- If water still flows, you have crossover somewhere
- Check single-handle faucets and mixing valves
When to Call a Professional
Some water heater issues require expert help:
- Gas valve replacement: Involves gas lines
- Tank leaks: Usually means replacement needed
- Code compliance: New installations may require permits
- No clear diagnosis: Multiple possible causes
- Uncomfortable with gas or electrical work: Safety first
Water Heater Lifespan
Most water heaters last 8-12 years. If yours is older and having problems, replacement may be more economical than repeated repairs.
Signs it’s time for replacement:
- Age over 10-12 years
- Visible rust on tank
- Water pooling around the base
- Multiple component failures
- Inadequate capacity for current household
Next Steps
If your water heater makes strange noises, see Water Heater Noises Explained. For general low water pressure issues, check our troubleshooting guide. Complete water heater maintenance instructions are in our Plumbing Fixes Guide.