If your residential gas water heater isn't heating effectively, replace the gas control valve. The gas control valve controls the flow of gas sending a signal to the pilot light, which heats the thermocouple (temperature sensor) and the burner.
A defective valve must be replaced. You can replace the valve yourself, but it involves working around natural gas. Here are some safety precautions and tips to replace a gas control valve on a gas hot water heater.
Prepare to Work
For this project, you need:
- work gloves
- pipe wrench
- plumber's tape
- replacement gas valve
If you smell gas, do not attempt this repair until you contact the gas company to find the problem. Blow out the pilot light. Look for the gas control valve on the outside of the heater at the bottom, and switch it to "Off" mode. On some models, you may need to press a button to turn the knob.
Rotate the handle on the water valve on the incoming water pipe clockwise to shut off the cold water. Open a hot water tap to prevent air pressure buildup. Let the water heater cool for about an hour.
Drain the Tank
Draining a water heater will help get rid of any sediment and prevent scalds from boiling water. Find the drain valve on the bottom of the water heater.
Turn the knob left, attach a garden hose and empty the water in the tank into a nearby tub, sink, or outside. Turn the drain valve to the right to close it and detach the hose.
Replace the Old Gas Control Valve
Remove the gas flex hose connected to the gas valve. Disconnect the nuts on the pilot, thermocouple, and burner tubes coming from the valve with a screwdriver or pliers and remove the tubes. Set the connection hardware and tubes aside. Check the tubes for damage and replace them if needed.
The gas control valve is connected by screws or nuts. Loosen the connectors with pliers or a screwdriver. Remove the valve and use it as a guide to buy a replacement from a home supply store.
Wrap plumber's tape around the connection threads of the new valve to form a water-tight seal; skipping the first two or three threads. Skipping threads prevents the tape from entering the unit.
Reinstall the three tubes you removed earlier and the gas flex hose. Attach the valve using the pipe wrench, making the connection tight enough to prevent leaks.
Restore gas and water to the water heater and check for leaks. If you don't trust your skill, or the water heater still doesn't work, contact a professional like those at Brother's Plumbing.