Water Heater Not Heating? How to Diagnose and Fix It

Reviewed by homemd.ai editorial team · Last updated: March 21, 2026

1. Diagnose: What Type of Water Heater?

2. Fix: Relight the Pilot (Gas, Standing Pilot)

This is the most common fix. Takes 5 minutes.

1. Turn the gas control knob to OFF. Wait 5 full minutes for any residual gas to clear.
2. Smell for gas. If you smell rotten eggs, do NOT proceed — leave the house and call your gas company.
3. Turn the knob to PILOT.
4. Press and hold the pilot button (or push the knob in, depending on model).
5. While holding, click the igniter button repeatedly until you see a small blue flame through the viewing window. If there's no igniter, use a long BBQ lighter at the pilot tube.
6. Keep holding the button for 30–60 seconds, then slowly release. The flame should stay lit.
7. Turn the knob to ON. You should hear a soft "whoosh" as the main burner ignites.
8. Wait 30–60 minutes for the water to heat up.

After relighting the pilot, wait 30-60 minutes before testing hot water

3. Pilot Lights But Won't Stay Lit?

If the pilot goes out as soon as you release the button, the thermocouple is bad. This is a $10–$20 part and a common DIY fix.

1. Turn gas to OFF and let it cool.
2. The thermocouple is the thin copper tube running from the pilot area to the gas control valve.
3. Unscrew it from the gas valve (wrench, not pliers).
4. Unclip it from the pilot bracket.
5. Install the new one — same route, same connections.
6. Relight the pilot and test.

4. Electric Water Heater: No Hot Water

1. Check the breaker — electric water heaters are on a dedicated 30-amp or 40-amp breaker. Reset it if tripped.
2. Press the reset button (high-limit switch) on the upper thermostat. Remove the top access panel, push the red button.
3. If it keeps tripping, the heating element is likely burned out — $15–$30 part, but replacement involves draining the tank.

5. Parts You Might Need

Honeywell Universal Thermocouple 24" — ~$12 — View at Home Depot

Rheem Universal Water Heater Element — ~$20 (for electric heaters) — View at Home Depot

Tools: Adjustable wrench (thermocouple), element wrench (electric element), long BBQ lighter (relighting pilot).

6. Cost Breakdown: Repair vs Replace

Rule of thumb: If the tank is over 10 years old and the repair costs more than $500, replace it. A new tank lasts 10–15 years.

7. When to Call a Professional

• You smell gas — leave immediately, call your gas company. Do not flip switches or use your phone inside.
• Electronic ignition system with error codes — these are harder to DIY.
• Water leaking from the tank bottom — the tank is corroded internally and needs full replacement.
• You're not comfortable working with gas lines.

FAQ

Why did my water heater pilot light go out?
Common causes: a draft blew it out, the thermocouple is failing, or the gas supply was briefly interrupted. Relighting it usually solves it. If it goes out again within a few days, replace the thermocouple.

How long does a water heater last?
Tank water heaters last 8–12 years on average. Tankless units last 15–20 years. If yours is approaching that age, start budgeting for replacement.

Should I repair or replace my water heater?
If the tank is under 8 years old and the repair is under $500, repair it. If it's over 10 years or the repair is over $500, replace it. A leaking tank always means replacement — it can't be patched.

How much does a new water heater cost installed?
$1,200 to $2,500 for a standard 40–50 gallon gas tank installed. Electric is similar. Tankless units cost $2,500 to $4,500 installed but save on energy bills long-term.

Frequently Asked Questions