How to test & replace a water heater thermostat so you can get hot water again

Is your water heater running cold? If you’re noticing inconsistent water temperatures or no hot water at all, a faulty thermostat could be the culprit. Whether you have an electric or a gas water heater, you can replace the thermostat without having to call a repair technician. 

If you need any replacement parts for your water heater or other appliances, you can enter your model number at AppliancePartsPros.com to order them. Most orders arrive in just two business days, and we have thousands of free guides to show you how to install your new parts.

Note: The information provided in this article may not apply to your specific appliance model. While we strive to offer helpful advice for DIY appliance repairs, variations in models and configurations can lead to differences in troubleshooting steps, error codes and part replacements. For the most accurate guidance, we strongly recommend consulting the technical sheet for your specific appliance model.

What causes a water heater thermostat to fail?

Water heater thermostats control the temperature of the water in your tank. When the thermostat malfunctions, your water heater may stop producing hot water or overheat.

Some of the most common reasons for a thermostat to fail include:

• Normal wear and tear
• Sediment buildup from hard water, which settles at the bottom of the tank and causes damage to internal parts
• Electrical issues like power surges or faulty wiring

Safety precautions

When working on any appliance, remember to keep safety first. Here are some tips to keep in mind: 

• Always power off and unplug your appliance or switch off the circuit breaker before you attempt any maintenance or replacement work. This keeps you safe by eliminating any risk of electric shock. 
• If the appliance has recently been used, give it plenty of time to cool down before working on it. 
• If you have a gas model, shut off the gas supply to prevent any leaks while you work. 
• Take your time while working to prevent accidents and personal injuries. Rushing is the enemy of precision.
• Work in a well-lit area so you can see and access appliance parts.
• Keep your workspace free of clutter and other obstacles. Keep children and pets away from the work area.
• Never work on internal parts with wet hands. Make sure the work area is completely dry.
• Check the user manual to see if there are specific installation or safety instructions related to your appliance or replacement part. 
• Be gentle when handling or removing parts. Excessive force might damage the appliance or cause personal injury.
• Wear insulated work gloves to protect your hands from sharp metal parts and debris.
• When working with wires, avoid touching any exposed wires or terminals. If you need to touch a wire, use a non-conductive tool or wear insulating gloves to prevent electrical shock.
• Always take photos or make a note of wiring terminals or other connections before disconnecting them to make reassembly easier.

How to replace a thermostat on a water heater

In most electric water heaters, you’ll have two thermostats: an upper thermostat and a lower thermostat, and either one may need to be replaced. Gas water heaters typically have a thermostat that can be found near the gas valve. Before you swap out the thermostat, you’ll want to test parts with a multimeter to make sure they’re faulty.

What you need

• Flathead or Phillips screwdriver
• Multimeter
• Insulated gloves
• New thermostat (make sure it’s compatible with your specific water heater model BEFORE installing)

Step 1: Turn off the power and/or gas supply

For an electric water heater: Turn off the power at the circuit breaker. 

For gas water heaters: Turn off the gas supply by switching the gas valve to the “off” position.

Step 2: Access the thermostat(s)

On electric water heaters: 

1. Find the upper and lower thermostats behind the access panels on the side of the tank. 
2. Remove the panels using a screwdriver.
3. Carefully pull back any insulation to expose the thermostat and hot water thermostat wiring.

On gas water heaters: 

The thermostat is often integrated with the gas control valve. It’s usually located near the base of the water heater.

Step 3: Test the thermostat

1. Set the multimeter to measure continuity.
2. Touch the meter leads to the thermostat terminals. 
3. Check the reading and refer to your unit’s user manual or technical sheet for the acceptable reading. If there’s no continuity, then the thermostat is bad and needs to be replaced.

Step 4: Disconnect the wiring

If you’ve determined that the thermostat is bad, take a photo of the thermostat wiring to help you rewire it correctly later. Then disconnect the wiring, unscrew the terminals and remove the old thermostat.

Step 5: Install the new thermostat

1. Place the new thermostat in the same position as the old one.
2. Reconnect the wires to the corresponding terminals by referring to your earlier photo or a wiring diagram for accuracy.  
3. Secure the new thermostat with the screws.

Step 6: Replace the insulation and cover

Once the new thermostat is installed, put the insulation back in and secure the access panels. 

For gas water heaters, follow the manufacturer’s instructions for reconnecting the gas valve.

Step 7: Turn on the power or gas & test the water heater

If you have an electric water heater, you’ll need to restore power at the circuit breaker. For a gas water heater, turn the gas back on and relight the pilot light according to the manufacturer’s instructions.

Allow the water heater about an hour or two to reach the desired temperature, then try running hot water to see if it’s working correctly.

Water heater FAQs

Get answers to common water heater questions here.

How do I know if my water heater thermostat is bad? 

Signs of a bad thermostat include:

• Inconsistent water temperatures
• No hot water
• Water is too hot

What is the cost of replacing a water heater thermostat? 

The price of replacing a water heater thermostat replacement cost can vary depending on the model. Replacement parts typically range from $20 to $300, while professional installation could add labor costs between $100 to $200.

What do I do if my water heater isn’t staying hot?

You may need to flush the tank, replace the heating elements, or see if your water heater is big enough for your home’s needs.

More DIY resources

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