How to Replace a Water Heater Gas Valve – DIY Tips

Knowing how to replace a water heater gas valve is essential for maintaining the efficiency and safety of your system. In this guide, we’ll cover the basics of what a gas valve does and how to change a Robertshaw or White-Rodgers gas valve in your gas water heater.

The gas valve is a critical component that controls the flow of gas to the pilot light and main burner in your water heater. Its job is to ensure the burner operates properly and safely, making sure your water heater functions as expected.

Here, we’ll dive into the specific steps for removing and replacing the valve, as well as the anatomy and key features you need to know for a smooth process.

Water Heater Gas Valves: Types and Features

Many top water heater manufacturers, including AO Smith, Bradford White, and the American Water Heater Company, rely on White-Rodgers and Robertshaw gas control valves for their systems. Other well-known brands, like Honeywell, use their own proprietary gas valve systems.

Understanding the different types of valves used in these heaters can help you make more informed decisions when it comes to maintenance or replacements.

Features of the White-Rodgers Water Heater Gas Valve

• Gas valve assembly with the safety valve, thermostat valve, and electromagnet
• Valve control knob with ON-OFF-Pilot settings
• Water temperature dial and setting indicator
• Inlet and outlet
• High limit or temperature probe
• Pilot tube threaded port
• Thermocouple threaded port
• Thermal switch

Features of the Robertshaw Gas Control Valve

• Gas valve with the safety valve, thermostat valve, and electromagnet
• Control knob with ON-OFF-Pilot settings
• Reset button
• Water temperature dial and setting indicator
• Inlet and outlet
• High limit or temperature probe
• Pilot tube threaded port
• Thermocouple threaded port
• Thermal switch

Anatomy of a Gas Control Valve

If you’re wondering how to replace a gas control valve, it’s helpful to understand a bit about its structure first. Some gas valves are equipped with a manifold gas pressure tap, which allows you to measure the pressure on the line that supplies the main burner. To do this, you simply remove the plug and attach a gas gauge to take the reading.

You’ll find the recommended pressure clearly marked on the water heater gas valve, so you can ensure everything is set correctly.

Both the pilot light tube and the tube from the main burner are connected to the gas valve. Also, a thermocouple is part of the system, acting as the safety element. The gas valve operates on 24 VAC but is also designed to function without external electricity, providing added reliability and safety in various conditions.

Temperature Setting Indicator

A temperature setting indicator, installed on the front of the gas valve, allows you to select the right hot water temperature. The temperature is factory set on its lowest setting to comply with the safety regulations. On some control valves (Robertshaw), there is a “HOT” mark which shows where the 120 F temperature or scalding water range starts.

Ignition

The pilot burner is lit by switching the control knob to the pilot setting (or pressing the reset button on Robertshaw gas valves) and pressing the piezo igniter button. There are some old water heaters where you have to use a match to ignite the pilot manually.

Thermocouple

When the standing pilot is lit, the flame will heat the thermocouple, which will generate a small electric current sufficient to keep the gas valve open, and once you release the knob, the gas will continue to flow to the pilot.

Thermostat

Then, the incoming cold water temperature will activate the thermostat that initiates the water heater gas valve to open to the burner. The pilot light ignites the gas on the main burner. Hot water temperature rises, and once it reaches the set temperature, the thermostat interrupts the main flow.

Energy Cut Off – ECO 

Two metal probes are mounted onto the back of the gas valve and immersed inside the tank.

The longer temperature probe contains a metal rod or Energy Cut Off (ECO) switch that expands and contracts as the water changes its temperature. The probe acts as the temperature high limit. If water gets excessively hot, a sensor within the probe opens interrupts the small electrical current to the gas valve, interrupting the flow.

Thermal Cut Off – TCO

A thermal Cut Off Switch or TCO is a resettable thermal switch designed to shut off the gas supply if there is a high temperature inside the combustion chamber.

Note: If subjected to excessive pressure (over 0.5 psi), the control valve gets damaged, resulting in gas leaks or, even worse – explosion.

A manual shut-off valve in the gas supply line should be installed together with the drip leg or sediment trap to prevent foreign material like dirt from coming into the control valve. A flexible pipe or ground joint union between the shut-off and water heater gas valve should be installed to allow easier service.

Note: If for any reason the heater fails to shut down, i.e., due to overheating, always manually turn the water heater gas control valve off.

Understanding How a Gas Water Heater Works

Gas water heaters operate by drawing cold water into the tank through the dip tube, which connects to the cold water supply. Inside the tank, the thermostat probe—part of the gas control valve—monitors the water temperature. When the thermostat detects that the water temperature is below the desired setting, it signals the gas control valve to open.

When planning to replace or change a gas control valve, it’s crucial to remember that in models with a pilot light, you must first activate the pilot by setting the control knob to “pilot mode.” Once lit, the pilot receives a continuous gas supply, regardless of whether the thermostat calls for heating. The gas control valve, however, only releases gas to the burner when heating is needed.

As gas flows to the burner, it is ignited by the pilot light, initiating the heating process. A thermocouple, part of the pilot light assembly, ensures the flame remains lit. If the flame is extinguished, the thermocouple cuts off the gas supply, shutting down the system for safety. The thermocouple generates a small electrical current that keeps the gas valve open as long as the flame is present.

When the water temperature reaches the level set on the thermostat, the gas flow to the burner stops, halting the heating process.

How to Replace a Water Heater Gas Valve: A Step-by-Step Guide

When replacing a water heater gas valve, use the factory-authorized replacement parts only. Exercise caution when handling the gas valve; avoid using a pipe wrench or similar tools to grip the valve body, and do not apply excessive force, as this could damage the unit. Both removal and replacement require disconnecting gas piping and electrical wiring.

1. Turn Off the Gas Supply: Locate the manual shut-off valve on the gas line, usually found near the water heater, and turn it off to prevent gas flow.
2. Adjust the Thermostat: Set the thermostat on the control valve to the lowest setting to minimize any residual gas in the lines.
3. Disconnect Electrical Power: Ensure that all electrical power to the unit is turned off at the circuit breaker to avoid any electrical hazards.
4. Set Control Knob to OFF: Turn the control knob on the water heater to the OFF position to stop any gas flow to the burner.
5. Drain the Water Heater (if necessary): If required by your model, drain the water heater to reduce pressure and prevent any water spillage during the repair.
6. Disconnect Gas Line Components: Carefully disconnect the thermocouple, pilot tube, main burner supply tube, and piezo igniter. Make sure to label or take photos of the connections for easy reassembly.
7. Unscrew the Gas Valve: Using the correct tools, disconnect the ground joint union and any other connections that are attached to the old gas valve. Remove the gas valve assembly from the tank.
8. Prepare the New Gas Valve: Compare the new valve with the old one to ensure correct specifications such as model number and ratings. Apply approved Teflon tape or pipe sealant on the threads of the new gas valve to prevent leaks. It’s crucial to wrap the tape clockwise around the threads to ensure a tight seal.
9. Install the New Gas Valve: Carefully screw the new gas valve into place. Ensure it is securely fastened but avoid overtightening, which might damage the valve.
10. Reconnect Gas Line Components: Reattach the thermocouple, pilot tube, main burner supply tube, and piezo igniter. Refer to your labels or photos to ensure correct reassembly.
11. Test for Leaks: Once everything is reconnected, turn the gas and power back on. Apply a soap-water solution to the new connections and observe for any bubbles that might indicate a gas leak. If you see any bubbles, turn off the gas and tighten the connections before testing again.
12. Final Checks: Once you confirm there are no leaks, set the control knob to the ‘Pilot’ position and follow your water heater’s instructions to relight the pilot light. Set the thermostat to your preferred temperature and check the operation of the water heater.

Safety Note: If at any point you are unsure or uncomfortable with performing these tasks, it is advisable to contact a qualified professional. Knowing how to replace a water heater gas valve is important, as it involves working with gas lines and potentially hazardous conditions if not handled properly.