How to Fix a Water Heater That Is Not Heating

If you turn on the hot water and nothing but cold water comes out, your water heater has stopped heating. This is one of the most common water heater problems homeowners face — and in most cases, you can fix it yourself without calling a plumber.

This guide walks you through the most likely causes and how to fix each one, step by step.

Why Is My Water Heater Not Heating?

Before you start troubleshooting, it helps to know what type of water heater you have:

• Electric water heater — uses heating elements and thermostats
• Gas water heater — uses a burner, pilot light, and thermocouple
• Tankless water heater — heats water on demand, no storage tank

The fix depends on the type. Let's go through each one.

Electric Water Heater Not Heating: How to Fix It

Electric water heaters have two heating elements — an upper and a lower one. If either fails, you'll lose hot water.

Step 1: Check the Circuit Breaker

Go to your electrical panel and look for the water heater breaker. If it's tripped, reset it. Wait 30–60 minutes and test the hot water again.

Step 2: Reset the High-Limit Switch

Most electric water heaters have a red reset button on the upper thermostat. Press it firmly. If it clicks, the limit switch had tripped — this often happens after a power surge.

Step 3: Test the Heating Elements

If resetting doesn't help, the heating element may have burned out. Use a digital multimeter to test for continuity.

💡 Recommended Tool: AstroAI Digital Multimeter — easy to use, accurate readings, perfect for testing water heater elements.

How to test:

1. Turn off power to the water heater at the breaker
2. Remove the access panel and disconnect the wires from the element
3. Set your multimeter to resistance (Ω)
4. Touch the probes to the two terminals on the element
5. A reading of 10–30Ω means it's working; no reading means it's burned out

Step 4: Replace the Heating Element or Thermostat

If the element or thermostat is faulty, replace it. A tune-up kit that includes both elements and thermostats is the most cost-effective solution.

💡 Recommended Parts: EWH-01 Electric Water Heater Tune-Up Kit — includes two 4500W heating elements and two thermostats, fits most standard electric water heaters.

If you only need to replace the thermostat:

💡 Recommended Parts: EWH-00 Water Heater Thermostat — upper and lower thermostats included, fits most double-element water heaters.

Gas Water Heater Not Heating: How to Fix It

Step 1: Check the Pilot Light

Look through the small window at the bottom of your water heater. If you don't see a flame, the pilot light is out. Follow the relighting instructions on the label of your unit.

Step 2: Check the Gas Supply

Make sure the gas valve is open (handle parallel to the pipe = open). Check that other gas appliances in your home are working.

Step 3: Check the Thermocouple

If the pilot light won't stay lit, the thermocouple is likely faulty. The thermocouple is a safety device that keeps the gas valve open when the pilot is burning. A bad thermocouple shuts off the gas automatically.

💡 Recommended Parts: Resideo 24-Inch Replacement Thermocouple — fits most gas furnaces, boilers and water heaters.

Step 4: Check the Gas Valve

If the thermocouple is fine but the burner still won't ignite, the gas valve itself may be defective and needs replacement.

💡 Recommended Parts: Gas Valve 70000 BTU — 1/2" inlet size, compatible with most residential gas water heaters.

Tankless Water Heater Not Heating: How to Fix It

Step 1: Check for Error Codes

Most tankless units display an error code when something goes wrong. Look up the code in your owner's manual.

Step 2: Check Water Flow Rate

Tankless heaters require a minimum flow rate to activate. Make sure you're opening the tap fully.

Step 3: Check for Sediment Buildup

Mineral deposits can block the heat exchanger. Flush and descale the unit regularly.

Step 4: Check the Heating Element or Igniter

For electric tankless units, test the heating element with a multimeter. For gas units, check the igniter and flame sensor.

When to Call a Professional

Call a licensed plumber or electrician if:

• The breaker keeps tripping after reset
• You smell gas near your water heater
• The gas valve needs replacement
• You're not comfortable working with electrical components

Summary

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