Search guides

Fix a tank water heater that will not heat

We'll confirm the symptom, rule out power or gas supply, then isolate the cause—high-limit reset, thermostat, or heating element for electric; pilot light or thermocouple for gas—or tell you when to call a pro.

Troubleshooting · Home appliances
15–60 min
What you'll need
  • Multimeter (for electric continuity tests)
  • Screwdriver set (Phillips and flathead)
  • Screwdriver (to remove access panel)
  • Replacement thermostat or heating element (if tests show a fault)
Step 1 of 10

Quick triage — pick your path

Get started

Choose the option that matches what you see. You can jump straight to that section.

Show full guide

Steps

Goal: Confirm the symptom, rule out power or gas supply, then isolate the heating fault.

  • Run hot water at a faucet for one to two minutes. Check the temperature.
  • Good: The water stays cold or lukewarm—heater fault. Proceed to Check power or gas supply.
  • Bad: The water is hot—different problem (e.g. faucet mixing valve); check faucet or plumbing.

Check power or gas supply

Goal: Rule out power loss and gas supply issues before opening the heater.

  • Electric: Verify the circuit breaker for the water heater has not tripped. Electric tank heaters use 240 volts; both legs must be on. Reset the breaker if tripped.
  • Gas: Confirm the gas supply valve is on. Check the gas valve on the heater itself is set to pilot or on per the label.
  • Check the heater type: electric has a thick cord or junction box; gas has a gas line, vent pipe, and pilot light access panel.
  • Good: Power or gas is on. Proceed to Electric path or Gas path based on your heater type.
  • Bad: Breaker keeps tripping or you smell gas—evacuate immediately if gas smell; call 911 or gas utility from outside.

Electric path

Goal: Reset the high-limit and test the thermostat and heating elements on an electric tank heater.

  • Remove the upper access panel and insulation. Locate the red high-limit cutoff reset button. Press it firmly. Replace the panel and wait 30–60 minutes for the tank to heat.
  • If the high-limit trips again or the water still does not heat, turn off power at the breaker. Remove the access panels and insulation. Test each thermostat for continuity. Replace any that fail.
  • To test the heating elements, shut off the water supply and drain the tank (or below element level). Test each element for continuity. Replace any that show no continuity or visible breaks.
  • Good: You found and replaced the faulty part. Reassemble, refill, and test—the heater should produce hot water.
  • Bad: All parts test good but the heater still does not heat—call a plumber. If you are not comfortable with 240 volts or draining the tank, call a plumber.

Gas path

Goal: Check the pilot and know when to call a pro for gas valve work.

  • Remove the access panel at the bottom. Look for the pilot light. If the pilot is lit, run hot water at a faucet—the burner should ignite. If the burner does not light, the gas valve has failed—call a plumber.
  • If the pilot is out, call a plumber. Pilot and gas valve work require a professional. Do not attempt to work on the pilot yourself.
  • Good: The pilot is lit and the burner lights when you run hot water—the heater works.
  • Bad: The pilot is out or will not stay lit—thermocouple or gas valve; call a plumber. Do not work on gas valves yourself.

When to get help

If you smell gas, evacuate immediately. Do not turn on lights or appliances. Call 911 or your gas utility from outside. Do not call a plumber for an active gas leak—that is an emergency.

Call a plumber if:

  • The heater is gas and the pilot is out or will not stay lit (thermocouple or gas valve).
  • The heater is gas and the pilot is lit but the burner does not light when you run hot water (gas valve).
  • You have replaced the heating elements and thermostats and the electric heater still does not heat.
  • You are not comfortable working with electricity or gas.

Verification

  • Hot water reaches the faucet within one to two minutes of turning on the hot tap.
  • Electric: high-limit has not tripped again; thermostats and heating elements test good.
  • Gas: pilot light stays lit; burner ignites when you run hot water, no gas smell.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm symptom Verify hot water is cold or lukewarm; rule out a different problem.
  2. Power or gas supply Check circuit breaker (electric) or gas supply valve (gas).
  3. Electric — high-limit and elements Reset high-limit; test and replace thermostat or heating element if faulty.
  4. Gas — pilot light Check pilot; if out or will not stay lit, call a plumber.
  5. Call a pro Gas smell—evacuate, call 911 or gas utility from outside. Gas valve work or repeated failures—call a plumber.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Heater type (electric or gas)
  • Whether power or gas is on
  • High-limit / thermostat / heating element test results (electric)
  • Pilot light status (gas)
  • Steps already tried

Is hot water from taps cold or lukewarm?

Run hot water at a faucet for one to two minutes. Check the temperature. If the water stays cold or barely warm, the heater is not producing heat.

Run hot water at a faucet for one to two minutes. Good: water stays cold or lukewarm—heater fault. Bad: water is hot—different problem (e.g. faucet mixing valve); check faucet or plumbing.

Yes No

You can change your answer later.

Different problem

If the water is hot at the faucet, the heater is working. The issue may be a faucet mixing valve, a specific faucet, or plumbing. Check the faucet or call a plumber if needed.

Done

Is power on (electric) or gas supply on (gas)?

Electric: check circuit breaker. Gas: check gas supply valve and heater gas valve.

Electric: verify circuit breaker for the water heater has not tripped. Gas: confirm gas supply valve and heater gas valve are on. Good: power or gas on. Bad: breaker keeps tripping or gas smell—evacuate immediately; call 911 or gas utility from outside if gas smell.

Yes No

You can change your answer later.

Is the heater electric or gas?

Electric: power cord or junction box. Gas: gas line, vent pipe, pilot light access.

Check the heater. Electric: thick cord or junction box. Gas: gas line, vent pipe, pilot light panel. Good: you know the type. Bad: unsure—call a plumber.

Electric Gas

You can change your answer later.

Did the high-limit reset fix it?

Electric tanks have a resettable high-limit button on the thermostat. Press it and wait 30–60 minutes.

Remove the upper access panel and insulation. Locate the red high-limit cutoff reset button. Press it firmly. Replace the panel and wait 30–60 minutes. Good: hot water after wait—resolved. Bad: still cold or high-limit trips again—proceed to thermostat and heating element.
Question

Did the high-limit reset fix it?

Continue

You can change your answer later.

Do the thermostats and heating elements have continuity?

Test upper and lower thermostats and heating elements with a multimeter. Turn off power and shut off water before draining to access elements.

Turn off power and shut off water. Drain the tank (or below element level). Test each thermostat and heating element for continuity. Replace any that fail. Good: replaced faulty part—reassemble, refill, test. Bad: all test good but still no heat—call a plumber. If not comfortable with 240V or draining, call a plumber.

Yes (all good, still no heat) No (replaced fault)

You can change your answer later.

Replace faulty part and test

Replace the faulty thermostat or heating element with a matching part. Reassemble, refill the tank, and restore power. The heater should produce hot water within an hour.

Done

Is the pilot light lit?

Remove the access panel. Look for the pilot flame at the burner.

Remove the access panel at the bottom. Look for the pilot light. Lit: pilot on—if burner does not light when you run hot water, gas valve issue; call a plumber. Out: pilot out—call a plumber for pilot or gas valve work. Do not attempt to work on the pilot yourself.

Yes No

You can change your answer later.

Does the burner light when you run hot water?

Run hot water at a faucet. The burner should ignite.

Run hot water at a faucet. The burner should ignite. Good: burner lights—heater works. Bad: pilot lit but burner does not light—gas valve issue; call a plumber. Do not work on gas valves yourself.
Question

Does the burner light when you run hot water?

Continue

You can change your answer later.

Call a plumber

If you smell gas, evacuate immediately. Do not turn on lights or appliances. Call 911 or your gas utility from outside. Call a plumber if: the gas pilot is out or will not stay lit (thermocouple or gas valve); the gas pilot is lit but the burner does not light (gas valve); you have replaced the heating elements and thermostats and the electric heater still does not heat; or you are not comfortable working with electricity or gas. Never work on gas valves or gas lines yourself.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why would a tank water heater not heat?
Electric: a tripped high-limit cutoff, faulty thermostat, or failed heating element. Gas: pilot light out, bad thermocouple, or gas valve. Check power or gas supply first, then the heating components.
Can I fix a tank water heater that will not heat myself?
Yes, for electric heaters you can often reset the high-limit, test thermostats and heating elements, and replace faulty parts. Gas heaters: you can check if the pilot is lit, but pilot or gas valve work always requires a professional.
When should I call a plumber for a water heater that will not heat?
If you smell gas, evacuate immediately and call 911 or your gas utility from outside. Call a plumber if the heater is gas and the pilot is out or will not stay lit (gas valve or thermocouple), if you have replaced the heating elements and thermostats and it still does not heat, or if you are not comfortable working with electricity or gas.

Rate this guide

Was this helpful?

Continue to