Water heater bad gas valve

[matt832]

I've got a Sears water heater made by State, and it appears the gas valve is bad.  Pilot kept going out, replaced the thermocouple and it will light and run for a while then cut out.  Seems to be temperature dependent.  I keep my water hot but at lower settings the burner seems to stay on.  So I suspect a bad over temp sensor in the valve.

Question, this is a basic 40 gallon tank with a 40,000 btu burner.  Is there a generic, cheap replacement?  Tank is 12 years old, I expect another 8-10 out of it based on past experience.  Sears wants $124 for the valve delivered, and State wants more. 

Is there any other option to repair this?  I usually go for TOL units that are now running $500-$600, so I don't want to replace the whole unit yet.  I found similar White-Rodgers valves online from $39-$89.

[RegUS_PatOff]

I'm no expert in this forum, just trying to help.

Do you have the water heater model number ?

[dkpd1581]

1. Make sure that the thermocouple is in the flame correctly (too much or too little will affect the operation)

2. Clean the pilot light burner head/assembly

3. Make sure that you need a thermocouple and not a thermopile  - the valve should tell you how many millivolts are necessary to maintain the pilot valve coil

4. Measure the milivolts present while the pilot is engaged to make sure you have the correct amount

5. Check to see if there is any type of draft or air movement affecting the flame area

6.  Look for any unsual occurences on start up of the main burner that may affect the pilot on startup or shut down

7.  Run the water and force the tank into a call for heat and check the temperature limits to see if they are in fact breaking control voltage to the circuit and the valve.  Replace the tank thermostat or safety as necessary

8.  Drain the tank and make sure there is no sediment in the bottom that is insulating the water from the burner and causing an abnormal situation

[matt832]

It's model 153.338450    I got the replacement thermocouple at Sears and they say it's the reccomended replacement.  Since i turned the temp down it seems to stay lit.  I use my water in the 150 degree range, now it's in the 120's.  No like.....

[applianceman18007260692]

Get a no2 pencil with a good eraser and remove your thermocouple. Use that eraser to clean out the base of the hole where the thermocouple screws in. This will get rid of corrosive buildup. Then reinstall the thermocouple. Make sure the pilot flame hits the tip of the coppernickle probe for maximum electrical output. Let me know.

[matt832]

 Thanks for the tip, I'll try it.  I don't hold out too much hope since it seems to be temperature dependent, anything other then low to mid setting causes the gas to cut out.

[Pffester]

While you have it apart get a can of air (or a tank of Nitrogen) and blow out the pilot tube & pilot. You may have a weak flame caused by dirt or spiders.

[edcmaak11]

[user=16896]dkpd1581[/user] wrote:

1. Make sure that the thermocouple is in the flame correctly (too much or too little will affect the operation)

2. Clean the pilot light burner head/assembly

3. Make sure that you need a thermocouple and not a thermopile  - the valve should tell you how many millivolts are necessary to maintain the pilot valve coil

4. Measure the milivolts present while the pilot is engaged to make sure you have the correct amount

5. Check to see if there is any type of draft or air movement affecting the flame area

6.  Look for any unsual occurences on start up of the main burner that may affect the pilot on startup or shut down

7.  Run the water and force the tank into a call for heat and check the temperature limits to see if they are in fact breaking control voltage to the circuit and the valve.  Replace the tank thermostat or safety as necessary

8.  Drain the tank and make sure there is no sediment in the bottom that is insulating the water from the burner and causing an abnormal situation

 

dkpd, just curious, my pilot goes out sometime too.  How do I measure the voltage thermocouple or themostat?   Is there a Manual I can look into?  I got 3 water boiler I need to look into...  Thanks!

 

 

[dkpd1581]

To actually measure the output of the thermocouple it is easiest to use a digital multimeter set on DC milivolts.  Remove the screwed in portion of your thermocouple (that part that actually goes into the gas valve itself) and hold one meter lead end tightly against the outside part of the thermocouple.  If you have the alligator clips that go to the end of your meter leads it makes this part of the connection easier - if not no biggie.

Looking at the butt end of the side that screws inside of the valve you will see a little section dead center.  It will look like a different colored material surrounded by the outter casing that you have the other end clipped to or held by the alligator clip.  Touch the tip of your other meter lead (the unused free lead)against this material in the dead center/butt end.   Holding the two leads like this while the other end of the thermocouple (tip end that sits in the pilot flame) is in a flame like a candle will cause your meter to read a DC voltage.

A new thermocouple would read up to about 32 milivolts.  As they get older, the voltage will drop and when it gets to about 12-15 milivolts, its time to change them out.

Thats how to measure one for trouble shooting purposes; however, universal thermocouples at Home Depot or Lowes are so cheap and easy to install that its usually easier and less time consuming to just change them out.

Be advised that certain gas valves use what is called a THERMOPLILE which is essentially a gang of thermocouples tied together.  By tying a bunch of thermocouples together you can increase the DC voltage output to 300-500 milivolts.  The reason for this is that with that much DC voltage output, you can run a milivolt thermostat and a milivolt gas valve off of the thermopile.  That gives you all the DC electricity you will need to run your gas water heater off of the pilot light alone - you need no additional source of electricity( no house power, no battery power, nothing).  That is a really cool thing when you want hot water in a location that has no or insufficient electrical resources. 

To know for sure if your gas valve uses a thermocouple or a thermopile, you will need to only look at the name plate of the gas valve and it will tell you.

Hope this helps you a bit.  If your thermocouples are good and the pilot still wants to go out intermittently, look for drafts that may be coming down through the flue or for some other outside source of drafts.  Check and make sure that your pilot is adjusted correctly using the adjustment on the gas valve.  Clean the pilot tube and pilot burner head assembly...best of luck.