Tip & How-To about Water Heaters

How to Change the Gas Valve and Thermostat on a Hot Water Heater

If you are having trouble with the temperatures of your gas hot water heater fluctuating too much, or after changing the thermocouple of your gas hot water heater then you may need to change the complete gas valve and thermostat assembly. Also if you have changed the thermocouple and the pilot still will not stay lit, then the gas valve could be bad or the ECO (Emergency Cutout) may have activated and is open. This is a onetime device and cannot be replaced.


These instructions are for the older style gas valve and thermostat combination. These commonly have a large red knob that adjusts the temperature of the water. Also note that the burner tube nut for natural gas is right hand thread, but if you have LP or propane gas the burner tube nut is left hand thread.


The newer gas valve thermostat combinations that have come out recently are similar, but they have a well in the tank that the sensor slides into. The assembly is held fast with a set screw. With this type of gas valve and thermostat unit the tank does not need to be drained, but most of the rest of the change out is similar.

To change a gas hot water heater thermostat you will need to first buy a new gas valve for your hot water heater. The gas valve and the thermostat are integrated into one unit.

To replace the thermostat on a gas hot water heater you must follow these procedures....

1. Turn off the incoming water and drain the hot water heater.

2. Remove the pilot tube, the burner gas tube and the thermocouple from the gas valve. Turn off the gas line and remove from the gas valve.

3. Get a pump pliers or a wrench in behind the gas valve and turn the whole assembly CCW to remove it from the tank.

4. After applying pipe dope or tape to the new gas valve threads, turn the new gas valve into the tank by turning in a CW direction. Be careful not to damage the small wires to the ECO. They are the little red wires on the back. If you break them the assembly is irreparably damaged.

5. Reinstall the gas line, thermocouple, burner tube, and the pilot tube to the gas valve.

6. Fill tank with water. Make sure to open a hot water faucet and purge all air from the tank.

7. Check for leaks where the gas line hooks up with soapy water.

8. Relight pilot light and check operation.

9. Set the new temperature setting to a medium setting and then adjust the temperature to your liking from there and adequate time for heating completely

Posted by on

Water Heaters Logo

Related Topics:

Related Questions:

3 Answers

I have a Rheem PG50T9A gas hot water heater. We had hot water this morning. When I came home the pilot light was out and won't stay lit. Any ideas?


Hopefully just the thermocouple. The thermocouple is the small rod right next to the pilot light. The flame on the pilot heats up the thermocouple and keeps the gas valve on. You can replace it yourself. The thermocouple will be connect by a small nut on the underneath side of the valve, and you will have to pull the thermocouple out of the pilot assembly. Not an expensive part, you can get it at any hardware store. Hope this helps you .

Apr 21, 2011 | Rheem 50 Gallon FVR NATGAS Water Heater...

1 Answer

i have a reliance 501 propane gas water heater how do i change a thermostate


Hi,

To change a gas hot water heater thermostat you will need to first buy a new gas valve for your hot water heater. The gas vaive and the thermostat are integrated into one unit.

To replace the thermostat on a gas hot water heater you must follow these procedures....

1. Turn off the incoming water and drain the water heater.

2. remove the pilot tube, the burner gas tube and the thermocouple from the gas valve. Turn off the gas line and remove from the gas valve.

3. get a pump pliers or a wrench in behind the gas valve and turn the whole assembly CCW to remove it from the tank.

4. After appliying pipe dope or tape to the new gas valve threads, turn the new gas valve into the tank by turning in a CW direction. Be careful not to damage the small wires to the ECO. They are the little red wires on the back. If you break them the assembly is irreparably damaged.

5. reinstall the gas line, thermocouple, burner tube, and the pilot tube to the gas valve.

6. Fill tank with water. Make sure to open a hot water faucet and purge all air from the tank.

7. Check for leaks where the gas line hooks up with soapy water.

8. Relight pilot light and check operation.

9. Set the new temperature setting to a medium setting and then adjust the temperature to your likeing from there and adequate time for heating completely.

heatman101

Feb 23, 2011 | RELIANCE ELECTRIC WATER HEATER

1 Answer

hot water tank does not work when shower is on, it does however work when the faucet in bathroom is on. It quit working in the shower about a month ago.


  1. COLD MIX, HEATER DEACTIVATES
    If inlet water temperature is over 70°F due to geographic location, water maybe very hot out of the tap. This requires a lot of cold water to be added with it in order to attain a useable hot water temperature. The addition of too much cold water will overpower hot water demand from the tankless water heater. This slows the flow within the tankless water heater, decreasing it below activation point, which shuts off the heater. The end result is nothing but cold water coming out of the outlet. See: TWH E2-04 Overcoming fluctuating temperatures [PDF].
  2. FLUCTUATING WATER PRESSURE
    If the water pressure in the home is erratic and the water flow is not consistent while a tap is opened, then the temperature of hot water will fluctuate. The minimum water pressure for the home should be 30psi or greater. For people on well systems the minimum pressure range is 30-50psi. The use of a pressure reducing/regulating valve is an effective way to maintain constant water pressure to the water heater. Watts brand 25AUB- ¾" or N35B-¾" pressure reducing/regulating valves or equivalent is suggested.
  3. CHANGING FLOW RATE
    Major changes in flow rate can adversely affect the output water temperature of the heater. Increases from one major fixture running to multiple fixtures running at one time can cause the temperature to fluctuate. Stay within the heater's specifications. See: TWH E2-03 Outlet temperature vs. flow rate [PDF].
From the Bosch website.

Good Luck,
Gary

Dec 16, 2010 | Bosch PowerStar AE125 AE125 Whole House...

1 Answer

Fluctuating water temp. It is hot when I start the shower,


Iam guessing your using it faster than it makes hot water. May need a larger unit or a second one,in the system

Apr 10, 2010 | Eemax ELECTRIC DE-IONIZED TANKLESS WATER...

1 Answer

fluctuating temperatures


Sounds like there is not enough flow in order to keep the burner in the heater firing continuously

Jul 09, 2009 | Rinnai Webstone The isolator EXP tankless...

Not finding what you are looking for?

2,309 people viewed this tip

Ask a Question

Usually answered in minutes!

Top Water Heaters Experts

Donni Steen

Level 3 Expert

659 Answers

Brad Brown

Level 3 Expert

15478 Answers

Gil Shultz

Level 3 Expert

3368 Answers

Are you a Water Heater Expert? Answer questions, earn points and help others

Answer questions

Loading...